It's the same thing that drives people to want to experience sexual pleasure or have one too many drinks. We all want to experience the other, and to get out of our daily existence.
I'm an actor. My life as an actor depends on who sends me what. I'm just taking the best stuff that I can find that's sent my way, regardless of how big or little the paycheck is. I don't want to work for scale anymore. I'm at a point now where, no matter how good something is, I'm not going to kill myself and end up in the hole.