I don't feel that at all. If Musk is having an AMA on a topic, like the BFR, I feel that is better than an open ended AMA, since the signal to noise ratio will be better and I can go there to read about exactly the topic I'm interested in. I'm not particularly interested, for example, in questions about Musk's divorce or dating habits.

Perhaps they need to change the name of these on-topic AMAs, but Musk isn't selling BFR rockets to consumers, generally geeks are interested in SpaceX from a hobby interest point of view, and so the idea of marketing and brand promotion seems a little divorced from reality.

SpaceX isn't going to increase their launch contracts by entertaining AMA questions. My guess is, Musk likes engaging people and talking about the cool shit he's working on.