One of the reasons is the music was so gawd awful. I consider 70s music to be the Dark Ages of music, 80s to be the Renaissance and the 90s to be the Golden Era.
I'm the opposite. In my opinion, 1925-1936 was the Platinum Era and 1937-1964 was the Golden Era. With the onset of Beatlemania, the Dark Age began and the music got progressively worse. There are only a few songs that I like from the 1980's onward.