It's partly because of the City insurance pool. CIRSA.

A large part.

They supress and settle cases; then erase them via NDA's. Often retroactively removing them from social media for winning cases. That has a powerful effect on public consensus around policing issues.

If you've seen Alabama Solution they kinda hint that the settlements are disconnected from the C.Os. I suspect that's the issue with Policing in Colorado and it appears to be in all States.

When they make mistakes there is no feedback loop for correction.

In District 18, they won't even accept a complaint about officers or the Police Department. The AG's office does, but they won't release any complaints (Police or otherwise). Since they won't release complaints there's nothing to suggest they are using them as a feedback loop of any kind.

There are definitely bad cops.

I think we have a growing issue that Denver Metro police departments can't attract and retain enough good police.