You can't blame this on evolution. 10 generations ain't enough. It's a sobering and scary thought that the raw talent of a Bach and a Mozart are probably still out there, and all we've got is John Adams and Eddie Vedder.
FWIW, Bach wrote for the glory of God. Mozart wrote largely for money and fame. If you think Vienna in 1785 was less promiscuous than, say, Lincoln, NE in 2003, you should read some of Mozart's letters. I've never liked Beethoven enough to read much about his life.
Fair enough. But do you really think more sex with more music groupies will improve the quality of the musical compositions?
As you noted before, philosophy has gone bad, reduced to navel-gazing. (I think theology went bad, first, but that's another story). The larger culture, and its musical expressions, have followed. Music won't get better until the culture again recognizes and honors transcendent order. Until then, all we'll see for the most part is the music equivalent of Jackson Pollack paintings (or whatever is the closest commercial successful equivalent thereof).