The Bulls and Nets forums were not bigger than the Blazers forums. Sorry.
I agree, though, that losing their three biggest team-related forums really has to hurt. They have a reasonably strong general NBA fan base, seemingly, but they really isolated and drove off the Bulls, Nets, and Blazers fans pretty ridiculously.
One of their key issues, I think, is the quality of some of their moderators. Some of the people that were greens over there when the Blazers' exodus took place clearly had emotional immaturity issues and didn't respect posters that had more experience online and in real life than they did. It was a bad job of promoting the wrong people and, at least in the case of the Blazers community, it cost them thousands of posts and tens of thousands (hundreds of thousands?) of page views.
Ed O.