Art-as-job is an artifice we've instituted through the invention of copyright, whose purpose is to ensure that we live in a society rich with art. There is not and never has been any reason to believe that this system, though it may serve its purpose to some extent, actually captures or meaningfully quantifies the value of art to society. The "demand" for art is made-up in the first place, not an end in itself or a measure of an end itself.
That's not it at all. There are already tons of people doing it, so many that the incremental value of one more person is small. The low pay reflects that; it's a signal that you should consider other jobs that are more in demand.