Not to mention that it seems as if you're defining 'potential' as strictly a matter of intellectual difficulty/cognitive complexity. Why wouldn't bartending be something that allows you to develop a skill previously cast aside/undiscovered? It's something you want to do, it can help you grow as well, right?
My initial response was more in line with "maybe people don't want to run themselves into the ground (and existential crises) doing something just because it's their "greatest skill" or challenges their potential as defined in the classroom." Pretty pessimistic and with only a hint of projection.

In other words, I'm with you. Just because I could do something difficult/highly specialized, doesn't mean I should have to. For my own sake.
I'm also inclined to take Hive's position. It's easy to do something you have no passion for, just because it's socially/culturally respected and something you are good at- in the sense that there are so many institutional structures in place to facilitate it. Want to go to business school? There's tons of them. Want to learn how to run a wildlife preserve? Not so much. And that's not even accounting how people's indifference to your goals can throw more wrenches into your plans than you might think. But even if you are able to provide for yourself and take care of living needs, how long would you want to bother living that life? *shrug*
There's a part of me that thinks that people choosing professions that don't challenge them is as much a social issue as it is a personal one. I can only speak for my culture: education as an institution is as broken as the day is long. And that's gotta count for something.