It's something much more fundamental: the lack of a perceptible and coherent musical narrative from work's beginning to end, which is to say the lack of the work's saying comprehensibly something beyond and exclusive of commentary on its own processes and methods which are — or ought to have been and be — but the mere tools used in its making.And this (you should read the Justin Davidson quotation at Sounds & Fury):
To put the matter more bluntly and much less eloquently than Mr. Davidson, a musical composition absent a perceptible and coherent musical narrative from beginning to end is gibberish, and not music.(Justin's point is quite a bit subtler and more suggestive than ACD's matter put more buntly.)
As in so many things, one's personal experience of music is one's own. It's not necessarily universal. I don't have problems following Carter's narrative. If you can't, it's not necessarily Carter's fault.
I don't have a problem with the outright dislike of any particular style of music. We all have our own ears and preferences. I know people who can't follow a Mozart symphony and others who can't follow Wagner. As I've posted, I couldn't deal with St. Francois d'Assisse. I just don't happen to think it's Messiaen's fault.