There are a ton of jobs that need doing that probably no-one actually likes, like stacking shelves in a supermarket, sweeping the streets, waiting tables, and so on. There are a few more that people maybe do like, at least some of the time, but would probably rather be doing something else, like tending bar. If everyone doing those jobs quits to focus on their guitar or something, what happens? Well the demand for those jobs doesn't go away but now employers have to pay a lot more to attract people to work them. Which sounds pretty good until you realize that that feeds back into the cost and suddenly everything in the economy costs more and the BI doesn't stretch as far as it used to. Which rather defeats the entire point of the exercise.