Peer pressure, thin blue line, us against them mentality, and no one but no one wants to be the first penguin off the ice floe.
When the dam finally breaks there are going to be a lot of freshly unemployed (and often incarcerated) ex cops. And the remaining cops will be more like the ones we remember from our youth.
I understand, but the good ones can't then complain when the stench starts to stick them.