It's not the police union's fault that there is literally zero pushback against them.
Somehow Teacher unions have near zero power but cops can collectively bargain for the right to murder people to get a paid vacation.
It isn't because they have a union. Most of them don't have more than a high school diploma and minimal training. You can replace them with ease. A strike shouldn't even be considered a threat. They often can't strike, and their normal threat is work to rule, ie follow the law.
It isn't the police union that keeps judges from throwing the book at cops. It isn't the police union that keeps 40% of the country rabidly insistent that gently reforming police would turn this country to ash. It isn't the union that forces them to die in car crashes far more often than they ever face lethal violence.
A union isn't magically powerful and never can be. The employer can always just replace the members. Funny how that keeps unions in check for such skilled jobs as Teachers and Bureaucrats and Nurses and ATC employees, but for people who usually have just a high school diploma and a few weeks of training suddenly it's impossible call the strike's bluff? I hear TSA bodies are desperate for work.
It's a narrative. Police unions are allowed to exist to encourage you to hate unions. Police unions have correctly identified that nobody even attempts to push back against them and are simply doing their job: Advocating for their members. You aren't required to accept a Union's terms. America is chock full of better trained private security that would be happy to scalp a police force.
Hell, police departments are often run by political candidates. Why don't the pro-union ones just get voted out by supposedly anti-union people?