I think "long" is a matter of perspective. I have read 25k stories that took me all day, and felt like it took a week. I have read 228k stories that took little time (for me) and felt like they read so fast.

Quality of the writing. The fact that the author has taken the time to get it reedited and beta'd, makes it more interesting for me to read.

Due to brain problems, it takes me a while to read stuff. So I like having it all together. Otherwise, I forget what I am reading. :-/