Bristol is getting a life. That is why she is doing what she wants to do. She is also making $400,000.
I believe that figure might be overstated. From what I've read, unless they've increased the stakes for this season, those who participate each receive the sum of $200,000 with the winner of the competition receiving an extra $100,000. Despite the hard work involved, the base amount of $200,000 is a nice incentive.