AC is more than just a forum. Its an all arround information site. True it is need of a major overhauling, but it has articles, profiles, links to books you can purchase online, etc.
The forums themselves are very basic. A lot of people talk about adding subcategories for various types of fish, but it just spreads out the information more. Also, since AC deals a lot with general aquaria, many of the same questions are asked over and over. It's quite easy to do a search and find the same question you are needing an answer to has been asked before. Rather than post it again, people can just read what has already been said. I doubt it is so easy at MFK because of the nature of your subject matter(rare, exotic, etc) meaning that more in depth questions arrise and are not always satisfied by searching previous posts.
Im positive the problems the board had over the last 2 years play a roll in things as well, as neo pointed out.