It seems to me like artists of any kind will only work at jobs that are slightly below their potential or skill level. Producers are just so cautious that they would never hire anyone who 'might be able to do it if they really pushed themselves'. They want to know that you can come in and slaughter the job, absolutely do it with your eyes shut. So if you're hiring for a commercial shooting glamour, you want the guy who has done it two trillion times already and probably in reality is absolutely bored of doing it.
If that were always true, then there would never be any advances in film making (or anything else for that matter). Sometimes, if you have a good relationship with a director or producer, and they get a challenging job, they might ask you to come along, too. Sometimes you're doing something that no one has done before, and you have to innovate. I think you'll find that many successful people are always trying new things in order to stay on top of their game.