You've touched upon a very important point. There is huge antipathy on the part of /b/tards towards sites like icanhascheezburger, knowyourmeme, and others that profit off of content created on 4chan and shared for free with its users. /b/ is mostly shit, but there are nuggets of gold there and most /b/tards browse in order to witness their creation. /b/tards generally lament memes that go mainstream. Rickrolling became incredibly painful once the old media picked up on it (long before, really, but the cat was out of the bag), as did chocolate rain. Sites that capitalize on the content created by /b/tards for other /b/tards draw a lot of ire, and are frequently the targets of attacks.

In the same way, most /b/tards would leave if 4chan became anything resembling a legitimate business. There are far too many alternatives out there, and while moot is generally well-liked, not too many people feel a great sense of loyalty towards him. /b/tards have left in droves over far milder insults than trying to make money off them.

The other problem is the content on /b/. It's nearly impossible for moot to find advertising partners, given that gore, beastiality, and child porn are posted fairly regularly. Not many legitimate companies are will to risk being associated with that, so /b/ has had the same banner ads for months on end. I can't imagine they pay much.