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.
Depends on what type of incident; if it’s something like noise in the hall or smoking, my apartment management handles it and lets people know (assuming it’s warning territory).
I’d imagine for anything else, it’s a matter of not wanting to endanger people through escalation of non authority figures. I think you would have to have just cause to evict people, so having an official investigation would be imperitive.