Why has mainstream music become so unspectacular?

Since the late 70's there has been a gradual decline in the quality of
mainstream music to the point where it is almost unlistenable. There
was a brief high point in the early to mid 90's, but an even more
rapid decline since then. Everything now is so artificial and
contrived. What has happened to all of that creativity we had before?
These little kids who play guitar hero can even tell you that there
is nothing like those songs in today's music.

Even the Brits aren't contributing much besides friggin Adele and a
bunch of other Amy Winehouse clones who stand there and sing hooks to
studio-produced background tracks (and a bunch of low-talent
Radiohead clones like Coldplay and Muse).