It's so funny when people realize unions are just special interest groups
Yes a coal miners union fights to keep coal mines open and police unions fight to protect their members from consequences, there's no reason to expect them to conform to leftwing politics just because the left in general likes unions
So what is a confederation of different industries ? Why many of those confederation accept every industries but not cops association ?
Finally, people organized tend to have share some analyses and goals, and some of them appends to be left-wing. It's not u surprise than people struggling for their rights meat the same issues, and share some common interests. Being smash by cops for no reasons when you just want to keep your job is an example why organized workers consider that cops have not the same interests