First of all, I've seen Avery Brooks at a convention, and I thought he was very nice and quite open with the fans. He really had a good time, and told us so.
That said, Avery Brooks has never been lacking for work and he is not one of those Trek actors who cling to Star Trek like a toddler clings to a blankie because they don't have anything else on their resume worth having.
Brooks was successful before Star Trek, and he has been successful since. Perhaps not in the way YOU think he should have been successful (more Trek or scifi related projects seem to be a favorite measurement of 'success' around here), but certainly by the standards with which he himself measures success.
So he doesn't go to every Star Trek convention, eager to cash in on Sisko at every possible opportunity. Big deal. I respect him for that - certainly more than I respect Marina Sirtus, who, despite the fact that she's such a terrible actress that she can't get a gig which doesn't have 'Star Trek' in the name, bashes DS9 at every opportunity.
I respect Avery Brooks. Star Trek was a job, and he was done with the job years ago. He doesn't need a bunch of nerd-love at conventions to bolster his ego...nor his bank account.
Good for him!