Because celebrities are the most visible 'upper level' people out there? (Why upper class? Let's be honest, how many people want to see the ugliness of the world beneath them?*)
And no publicity is a bad publicity, they said.
Besides, it's a specific percentage of celebrities that reached the level of fuckedupness several Hollywood celebrities can achieve. They are just the most visible. I would say everyone has something bad that if exploited well every now and then, will result in the same exposure as Hollywood celebrities and socialites have now.
*On the other hand, it does make for a different kind of exploitation, doesn't it? See Starving Childrens of Africa, every Friday on Fox, afterwards see Women in Shackles : The Reality of The Oppressed Minority on CBS.
As long as people are taught to see and not feel, it won't stop.