That would be a very poor financial move for the forum. Signature campaigns increase traffic to the website, and in turn, the number of impressions that are seen by ads. Removing campaigns would result in a drop in traffic as well as a drop in ad revenue for the forum.
There's a balance to found in there somewhere. If every single poster is posting junk in search of dust, that's not going to make the advertisers any money. The more committed users will become disenchanted and shop elsewhere.
U're totally right. This "traffic" is useful to no one.
Both account sales (multi accounting included),and campaigns should be straight out forbidden. Quality over quantity. Until then, it's wild west.