Most police unions do not share the same social goals as a good portion of the labor movement at large. Most do not lend solidarity to unions when you see unions pushing whatever social agenda they are trying to push. Very few police unions have ever been active participants in the any form of the civil rights movement, in years gone or now, for instance.
Only when a police union finds itself in a contractual dispute with an employer or when their union's life is threatened do they act like most unions act. Coincidentally it is when they expect other unions to support them. When the state of Ohio pushed a right-to-work statute forward it failed to exempt police officers and firefighters. Consequently the FOP (and firefighter unions) came out in droves with the rest of the Ohio labor movement to defeat Senate Bill 5, and it died on the floor. Similar right-to-work legislation in Michigan and Act 10 in Wisconsin carved out police officers and guess what? The FOP and other unions exclusive to law enforcement were nowhere to be seen as unions massed to protest.
I have been involved with labor unions everywhere I have worked, at every level one can be involved and have been on staff at two different unions (one is my current employer). After decades of doing or being around this work I have very rarely seen any police union behave in a way I'd want a union I was involved in to behave.