It has some benefits for influencers to adopt it. On twitter, instagram, and youtube, the comment section is quite messy. If you're a big name, you'll be overwhelmed by questions, and same questions are asked over and over again. Going through all those questions to pick out important ones is tedious. This is basically a zendesk for them (if they want to engage with their followers). So you're right, like AMA, going from influencers' side probably has a better chance to bring the community up.

On the other hand, the fact that an important questions getting large number of thumb-ups is a statement by itself. Imagine a question for POTUS with 10k thumb-ups but got no answer from him/her. It's a headline material.