I think for most its a to be in "the in crowd" mindset. Not having enough to make it in the movies or on TV. Settling for "sloppy seconds" of stardom. It is a big industry and has large circles of "beautiful people" just as Hollywood does.
The thirst for fame and fortune is embedded in many girls at a very young age. Their plan starting already at that early age. To try to be one of the beautiful people. So they settle for it, trying to be the best they can. We as a society are constantly damaging little girls with what they see as demands on looks (breeding anorexia) and the pressure to fit in and be one of the "in crowd", look at HS cheerleaders and Prom Queens/Princesses. If you aren't one you aren't anything.
I don't think anyone has ever just woke up and said "When I grow up I want to be a Porn star." I feel a series of step by step leads them there , some model pics, then a few nude pics, one amateur short, then on and on. Building blocks. I personally find it disturbing that so many are indeed so beautiful and probably taking a bit more time could have made it big as top models or in commercials.
In some other cases, sadly they are drug addicts and prostitutes who get caught in a web of their own making, losing their identity as humans and "go with the flow" to survive.
I suppose some do make the choice to do it because they like sex a lot. I don't feel that number is very high though.
Just IMHO
