I think that some people have either had bad enough experiences themselves, or have heard of incidents, where they fear confrontation. By talking to someone who is engaging in an annoying (to you) or antisocial behavior, you are opening yourself up to retaliation by that person. If you just call the police anonymously then the target doesn't know who to retaliate against.

Of course, a much better strategy is to go out of your way to be neighborly, get to know the people around you. That way if someone is having a party a few houses down, instead of calling the cops you can grab a couple six packs and head on down and join them.