Seems like the staff has always been unwilling to add sub forums no matter how potentially useful and no matter how proven (on other forums). Before this was because there was no subforums feature so it'd be disorganized. Don't know about now.
^ Could it be, and I am just throwing a thought out there, that sub-forums tend to look tacky? Personally I have never liked sub-forums for that reason. I found it harder to find stuff and that it took more effort to get to certain threads. I always loved the organization of the site here in terms of the forums. I had another point to make as well, but I forgot.