I think the answer is - because they’re lazy and want you to do their dirty work for them. I quite frankly, am not going to call the police over noise complaints because I think management should do something about that. Police should only be called when violence or tenants who get aggressive.
Not because of noise, I just think it’s management dumping responsibility onto you when they’re the ones with the power to evict people.
While the details depend on the jurisdiction, in most of the saner places landlords can’t evict over something like noise. Your anger is misplaced.
Have you tried being an adult and camly talking to your neighbour? Let them know what you hear, how its impacting you and some respectful suggestions on how things can be made better.
Also what kind of noise are we talking about and when? Life makes noise, and you chose to live in an appt with thin walls. Some noise is to be expected.