But marcotheminer has exposed a logical point of view, if a lot of signature campaign will be banned the number of visits and posts will decrease (automatically). However, I don't think the most important thing here is the internal forum ads revenue.
Which is of pretty low importance. The number of anything is useless if it is of very low quality. BTCT should be a place of full of excellent discussions, not a place full of random posts.
I hope the number of useless and spammy will decrease, but without an interview of the admin I don't think the things will change.
From this viewpoint, the quality of content on BTCT has heavily degraded over time because of various reasons.
I agree with you, the sig campaigns are in the first place of the reason list (or at least them are the primary cause).