I think it's mainly personal preference in composer, player and listener. Just as authors seem to excel at either novels or short stories, so people like short or long forms, whether they are creators, performers or listeners. I'm a short form man myself , or more correctly stated, I can deal with long pieces provided there exist frequently changing, contrasting sections within them. It's not the time the things take to play but rather the grinding on of one musical idea which turns me off.
A good improviser who produces a constant kaleidoscope of changing ideas, whether related to one another in formally conventional ways or not, probably has my attention for as long as he cares to play. On the other hand, somebody playing a piece comprising three or four ideas, one and a half chords, umpteen repeats and the rhythm of a dirge had better be a presentable female in a short dress or else the pattern of holes in the ceiling tends to become frightfully interesting.
Many musicians and people I know really enjoy listening to long drawn out repetitious things though and good luck to them, to each his own - just as long as I don't have to sit through it.