Because they are usually white and Latino suburban cops or cops from white areas in cities that don't like Democratic-controlled City Councils or state Legislatures enacting too progressive reforms like a civilian complaint review board or ending qualified immunity. They feel it handcuffs them from doing aggressive policing. They feel the morale is low, that the progressive white/black/Latino/Native American community doesn't have their backs, the police command doesn't have their backs, the city mayor, politicians and media don't have their backs and with Kaepernick, that Kap, LeBron, Jaylen Brown, etc. don't have their backs, and those were guys they liked watching sports to escape.
In 1992, The NYC PBA and Rudy Giuliani had a City Hall riot to protest Mayor David Dinkins' proposed reforms.....