Hacking gets you nowhere. There's anti-hack plugins on most servers so you get kicked for flying. Most people know how to tell if someone's hacking and some people have the sense to tell staff, even if they don't have solid evidence.
As for why they do it... Maybe, if there's a coins system, they want coins easier or... They just want to be cool and win, even though they just make themselves really unpopular for doing it.