This is the ugliest form of brainwashing. That some schools require it is very frightening. Congratulations to those good souls who will serve a fellow human in need without reward and without boasting about it. But many do it to gratify themselves and even more because they're blackmailed by their schools to do forced labor.
I believe that community service has become a fashion statement/trend. I think it really stems from the fact people are inherently selfish. They want people to praise them for doing community service, not because of the fact that they're improving others lives or communities. They want to feel like they're a good person when probably deep down they aren't.
For high-school students, at least, community service has become more of a requirement in order to be accepted by colleges. While community service in and of itself is a good thing, some students go way overboard, sacrificing study time and recreation time to stack up the hours. Which makes community service a bit selfish (since it's to improve one's standing with colleges) but it's definitely not a fashion trend.