I recall discussing this with some one who had switched to web dev from music - he had a Phd and was a London Session musician who had played on top 10 hits.
At some point it stops being fun - 8 hour days practicing for example he mentioned.
Most professional musicians I've heard from would be thrilled to even spend that much time on music itself, what with all the other annoying business details to manage.
I think that's the story of trying to turn anything hobby-like into a living. You start out as a photographer or an artist, but you end up having to be a general manager and an accountant.
It's the age-old tension between "do what you love, and you'll never work a day in your life", and "the best way to ruin your hobby is to make it your job."
At some point it stops being fun - 8 hour days practicing for example he mentioned.