Just to preface, I am a cop. I don't hang out with cops, nor do I consider any cops good friends. But I do respect most of my co-workers. I just came into the profession later in life (mid-30s) and in a place I didn't grow up in. Also, every cop where I work lives in our jurisdiction; and we are not a small department (we are in the top 20 for size). Most cops, like most people just want to go to work and go home.
There are good cops, and I feel the majority fall under that category. Just like doctors, lawyers, teachers, etc... bad ones get through the cracks in all those professions. Ask any one in those professions if they know of any one in their office or network if there are members who shouldn't be there and they will probably say yes. I've yet to have one tell me no (that doesn't mean there aren't any out there that would). Now, if they are answering yes to that and they haven't done anything to get rid of that person are they not, per many of your opinions, 'bad apples' too? Perhaps you reading this falls under that hypocrisy as well.
Every year my department fires several dozen officers. This may be due to officer safety issues, too many personnel complaints (sustained) from the public, use of force violations, malingering, and a myriad of other reasons. I've never seen a 'whistleblower' get any kind of punishment, administratively. I have seen officers, and have been myself, iced out by fellow officers, though I've never not had back up show up to a call nor felt any unnecessary danger in doing my job. Generally guys would be butthurt a friend of theirs got in trouble but it blows over in a few weeks.

'Why don't good officers turn in the bad ones'?

I feel, and it's my opinion from 8 years of experience, that the good officers don't hang out with, nor witness, what the bad officers are doing. I admittedly know that it a weak argument but I'll try to explain. Think of your work bubble, if you work in a large office. How many people do you know, how many people's reputations do you know, and how many of those people do you work closely/socialize with? If you are able to have some control over who you work with do their reputations have an impact on that? I work, about 75% of the time with a group of 4 officers. I, through my performance reviews and reputation, was able to have some say in what unit I could join and who I'd be working with. All the members of my team have reputations within my department that are similar to mine. We don't take short cuts, we do our job, and we go home (I work with Neighborhood Security Watches about half the time and do homeless outreach and enforcement on community complaints the other half of the time, along with special projects here and there). The other 25% of my time is filling in on patrol for staff shortages and being a 'normal' cop.
When I'm doing the 'normal' cop thing I know who the officers are that I work with and they know me. Some will be nice, others just don't engage with me. And that's fine with me because I know their reputations. And here's the thing, bad cops don't like to work with good cops and the same is true reversed. What's the difference between the two: good cops, who I do believe are the majority, file their reports correctly and on time. They do their traffic stops per policy guidelines. They make checks of their beat to make sure abandoned cars are towed, they stop by businesses to say hi and see if they have any community concerns, they know, either by name or face, the homeless in their areas and attempt to build a rapport with them, or at least let my team know if they want shelter or social services or they see a new face. They make sure the traffic lights are working, the bus stops aren't cluttered, they know the problem houses and problem individuals and generally take pride in knowing what is happening in their area. They are just going about their shift until it is time for them to go home.
As for the bad/lazy cops: they go park and hide. They rarely do traffic stops, they don't know the neighborhood and they avoid areas where they may be flagged down for help or questions. They approach every contact as a problem, they work harder at cancelling a case than the amount of work it would take to just type it up, they avoid people because they don't want to be bothered, and they generally have the deescalation skills of a toddler. Not all of them are bad people, they just, like some people in every profession, are there for a paycheck and nothing else, even their actual job responsibilities. Of this group, the majority aren't going to cause problems, they just aren't that good at the job. But in this group you get the officers who want to 'be the man'. They may not be 'lazy' like some of the other bad cops, but any call that isn't a fight or in their mind a 'hero' moment is beneath them. These are the officers with the puffed out chest, believing everyone and everything is a threat and they are going to prove they are the toughest SOB on scene. They also, though, usually take shortcuts, forget key details, and rush through investigations that can lead to weak cases, public complaints, and lawsuits (though I seen enough lawsuits for incidents where every single policy and procedure was followed to know that they will happen no matter what).

Now why don't I, or officers like me do anything to get rid of these bad cops?

Let's go back to the other professions I mentioned above and whether or not the bad ones from those jobs were pushed out...from the people I've talked to they haven't. The reasons vary, but or comes down to the person I talk to doing their job and letting them do theirs. And it's similar to my experience. If a 'bad' cop gets sent to a case and I'm nearby, I will go and make sure the scene is safe, good cop or not, I don't want any of my coworkers to get hurt. But knowing that person's reputation, if the scene is safe and it's not a total shiatshow, I'm moving on to my next call or check, because I don't want my name of their report. Conversely if I'm off on a case and a 'bad' cop shows up, I'll tell them I'm good and don't need help, as I don't want their name on my reports either. It may come across as weak reasoning, but if I don't see it, I have nothing to report and I am not breaking any policy.
If there is no way to avoid working with someone like that I just need to make sure that I'm documenting, through my body cam and report, any actions that aren't being done per policy and report them to my supervisor, for if I don't I'm just as guilty of the policy violations as they are. After that it is on the supervisor, not me, to follow through with the complaint. And if the supervisor mishandles it at that point, our internal standards office, who must look at each complaint, may take action on him.
But these steps are done only if I see the violation, or have proof of a violation. If it's only rumors or hearsay, and I make the complaint and it's unfounded, then I can, and most likely will, face disciplinary action for making a false claim.
I know in my department guys face suspensions all the time for complaints brought about by other officers; improper labeling of evidence, late reports, incomplete reports and citations, forgetting to take photos, etc...are just some of the reasons guys have taken suspensions. It just doesn't make clickable headlines for news outlets "cop suspended without pay 1 day for forgetting mileage report" won't get a lot of clicks. And yes, all suspensions for behavior or negligence are unpaid at my department.

Now to ACAB, I don't have a problem with people who say it or believe it; many of them feel they were wronged by police at some point in their lives, or they don't like authority, or they truly believe police aren't needed. Whatever, it doesn't bother me for them to believe that. I do believe though that others have the same right to support law enforcement and the police. And you can fully agree with the message of BLM and other groups like that and support law enforcement; they don't need to be exclusive of each other. Holding law enforcement, or the protesters for that matter, accountable for their actions shouldn't take away from your support, it should actually strengthen that support.

It really is sad that 'reform' has such a negative connotation, as all businesses, including law enforcement, need to change with the times or get left behind. It sucks that 'reform' can't be changed to 'improvements', because that is what reforms should be viewed as. And hell, if I don't have to go to mental health, suicidal, or non criminal calls anymore, sign me up for those improvements (it's not that I don't care for the well being of people in those calls, I get only about 16 hours of training a year in those types of calls so it's not really fair for me or them to send me to those calls).

TL/DR: good cops outnumber bad cops; reforms are needed improvements, and shouldn't be viewed negatively.

austerity101: Reform hasn't worked.  You've had 200 years to get your shiat in order.

You're right, but in the 8 years I've been in my department we've instituted zero-tolerance for officer involved DUIs, physical domestic violence incidents, and use of force violations. We've taken out neck restraints from our use of force, mandated body cams, and even though our budget has been cut, have introduced a crisis response team and a community homeless team that works exclusively with our area's social service providers to re-direct homeless individuals that are repeat offenders for minor crimes and other violations. So, I can't speak to the previous 192 years, but I feel we've made some progress.

Look, I know that no one's beliefs are going to change because of some comment on a message board, but I try to look at most main stream media outlets, smaller niche outlets like TheRoot and others like it, liberal and conservative, and read people's comments, especially those that are different from mine to learn and see where the other side is coming from. I'm not perfect, you're not perfect, and no matter the system, it will never be perfect. I'm just trying to do the best I can in my own little area.