Why isn't VBForums.com, CodeGuru and whatever other forums Jupiter owns combined?

For example many sites like WMExperts and TreoCentral use one database for users and forums but each site has a specialized look, feel and forum layout.

So why wouldn't Jupiter combine forums? This would make maintenance much easier and we could have a set of consistent usernames, moderators and even banned users (rather than banning someone from each forum separately). Just seems to make sense to me.

I know it's doable since other companies do this but is it feasible with Jupiter's forums?