Bruce mentioned in an interview - which I can't find (maybe it was in the meetup) that he didn't know that the ANN section existed. ...Until Kai added it.
I really don't know the reason, and Kai make a great work until now, I prefer to think that it's not a "market strategy" or something similar, and of course kai don't need to be professional as he is only one user more and he could make as he want.
But the Bitcointalk ANN or simply "ANN IS PUBLISHED" (as they say in the Project Timeline in the WEB), it's not a minor question if you would a good community. And they failed in it.