Originally Posted by AndrewPd:
“I don't think Big Brother is the place to go to deal with your issues.”
One could say that about a lot of them, though. Nick's there as he feels friendless, has no job and wants to find friends and, as they all do, wants to potentially win some money. Jack's partially using the time as an alternative to Gamblers Anonymous

Everybody's got issues.
I don't think Cristian, or anybody, said they were there to deal with their issues, but I imagine that - over the course of the show - some issues may be dealt with one way or the other.
ETA: Wasn't Cristian the one who said he thought he should be on CBB? I think he's mainly there to up his profile, career-wise, as many of them are.