I'm not sure how that ties into your argument that nobody writes a great work for profit, but that has been my observation. I'm quite sure that if anybody today wrote a symphony that could compare with one written by Beethoven in the early 19th Century, he would be greatly rewarded monetarily. Why then, hasn't anything as good as Beethoven ever been produced in the past 100 years?
I would argue that across the arts, from sculpture to painting to music to writing, the 20th century lost track.
I guess it's aprtly due to the fact that while the nineteenth century focused on technical perfection, the twentieth focused on newness and difference.
In my opinion (and I realize I'm now moving into a purely personal realm of taste) the last truly great prose was written by Beckett and Robbe-Grillet.
I'll use them as an example. They both did very bold new things and violated the rules of grammar and narrative in their work. But they shared the nineteenth century notion of perfection: they carefully worked on their writing - every aspect of their work is intentional and fits into a larger whole.
The problem is, anyone else can now come along, write a jumble of hard-to-parse words nearly at random, and claim to be just as entitled to respect as a Beckett.
That's the paradox - if Beckett wanted to he could have written a near-perfect parody of Samuel Johnson or Cardinal Newman or any other great English prose stylist. In his work you can catch echoes and snippets of the KJV or Sterne. He knew perfectly how to write in a traditional, conventional way. Whereas "avant-garde" writers today could never do so - they do not have the craft, the skill and knowledge that Beckett had.
But throw hard-to-read prose by Beckett and by a scribbler in front of the average person and they will be equally unimpressed.
I suspect it's much the same with music: the really excellent musicians can interpret the classical tradition. But new movements like Serialism tend to eliminate all possibility of craft from music.
Beethoven is now so long gone, as is his world, that it would be tough to create music like his today without simply being labeled and old-fashioned rip-off artist.