Very few pilot scripts are purchased, and few of those get an actual pilot ordered, and even fewer of those ever make it to air. It's mostly useful as a writing sample, a way to get representation, or a way to get staffed writing on another show. The odds of the pilot I'm writing ever actually making it on air are tiny - I might as well play the lottery. But, it's part of what you do if you want to write in film/tv.

:/