I strongly dissagree with the age reasons suggested. I am 39 and althouhg I do no regularly listen to chart music, I do listen to some and there have been new songs that I have really enjoyed. These are a couple of years old now but Strange Glue by Catatonia as a song that I particularly enjoyed and I also found some of Space quite interesting and enjoyable.I do not believe that the question revolves around people getting in set ways as they get older and I would happily join a folk rock/ folk punk or whatever mix if we had the personnel around here to do it.
I still believe that the truth is that so many people just go with whatever is the in thing and that this is not based on anything musical.
Jon