You have to start with the villains here, as some of the most popular reality shows (and "reality" shows) are all villains, like The Hills and Jersey Shore, which apparently people watch by the millions just to stare at people they hate.
The same reason Grey's Anatomy promos keep promising you one of the characters is going to die.
This why people from around America will watch a Dallas Cowboys game, in the hope that someone gets hurt. Dallas is consistently the most hated team in the NFL, a phenomenon I have explored scientifically using charts.
All the stars aligned a few years ago when the NFL's most hated concentrated mass of douchiness, Terrell Owens signed with the Cowboys. When not publicly insulting his less famous teammates, or publicly outing the guy who throws him the ball so he can continue to make millions of dollars and who isn't gay, Owens is well known for classy touchdown celebrations like hurling snow at the fans, tearing down fan signs and dumping a fan's popcorn into his helmet. If this were reality TV, you would have immediately assumed it was staged.