Recently I let a friend of mine read my latest story before I published it. He came back with feedback that I hear a lot about not just my comics, but comics in general. "It's too short. It needs more character development. It needs more backstory."
Almost every negative comment I get has to do with length and the fact that characters aren't "completely developed". I blame TV and movies. TV shows with "fully developed" characters tend to run in the hour range (with 15 minutes for commercials). Movies typically run 90-120 minutes. That's roughly 6-8 typically comic book issues. My friend has written a screenplay (like so many others) and while he did it, he obtained a lot of guidance from someone who has sold screenplays. He basically learned the formula (you must have certain elements, they must be introduced by a certain point in the movie, etc.) Commercially successful movies tend to follow the same formula, and I think people have come to expect that in everything and have actually subconsciously set that as the criteria against what all other media is judged. A lot of novels have gone to the "screenplay" format to both attract readers and movie studios for this reason. So when you try to do something different (like tell a short story or focus on something other than the main character's backstories) people assume that it is "bad" because it isn't what they've come to expect.
Not everyone does this. Some people realize there are different types of stories, such as the concept story, and developed characters actually detract from that. I personally get a little bored with the traditionally formula that is used so often. It makes it so much easier to predict the twist endings, and while that's fun, it gets old after a while.
That's one reason I decided to go with 80-pages for a story instead of the traditional 18-22. It allows a much more developed story in one sitting that you don't have to wait until the next issue to continue. That break can be jarring.