Well, there are issues of organizing and abbreviating... You don't necessarily want to show a hundred images on one page, and if they're all in one post, figuring out how to hide them is a bit more complicated, although of course not impossible.

I think the real argument, though, is that image boards are for discussions of images, not image sets. The mentality of thinking in image sets is more for porn collection than for the kind of visual culture we might want to encourage.