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.
Can you explain what’s unreasonable about that? External noise may be outside of their control but that doesnt mean they don’t bear some responsibility to ensure that residents have peace and quiet in the place they’re being charged to live. In that scenario, you would typically have the right to break your lease and move out without penalty. With internal noise, they have the responsibility to penalize the noisemaker with fines or eviction.