I LOVE all the short fic--so much of it (on lj) is so very good! But there's nothing like a longfic. I prefer novels to short stories, TV to movies, etc. So it's a matter of preference.

And the time commitment needed for writing or reading long fic is probably outside of many kpop fan's ability?

Maybe! I know I was reading longfic when I was...13/14, but maybe kids are different now, and writing a long one yourself IS a big time commitment.