Here's a fun little theory:
Art communicates to people. If it is really good, it even communicates to people who have not seen it directly in the physical world, and maybe other kinds of spirits and places.
The parts that communicate most directly to humans are what makes it succesful commercially.
The other parts don't, but they are more important because they influence the whole world.
Thus the conflict of the artist.
UPDATE: I am not being clear. Another attempt:
An artist has a contract with god and the universe. And a relationship with humanity. These two can conflict. In the rare, most brilliant art they can work in harmony.