I'd fully expect "11 reasons people speak at conferences" to include a lot of reasons associated with personal benefits. (And I'd actually only count 3 of those as being vanity: the rush, promotion, and recognition.)

People sure don't speak at conferences so they can spend more time at airports and on planes.

Many do also enjoy it for altruistic reasons listed. But relatively few people are going to take on tasks that aren't also beneficial to themselves personally.

I think this is a fair critique. Many people who are drawn to public speaking probably tend toward the "vain" side of the personality spectrum.

Anecdotally, I acted in a play when I was in college. Almost every person in it was studying acting, and the level of self-absorption was overpowering at times.

All that said, speakers and topics are only a small portion of what I find valuable about attending a conference anyway. Most of the opportunity for learning and advancement comes in meeting other people you wouldn't have been able to connect with otherwise.

Whether or not it's vanity, there's an element of enjoying being in the public eye--at least in some contexts. If someone really doesn't like being publicly visible they're mostly going to self-select out of being a speaker unless they have some other compelling motivation for doing so.

Whether or not it comes naturally or it's a persona they've developed for professional reasons, most public speakers like the energy of the crowd or other audience. (Personally, I'm much more comfortable live than on video--which is a somewhat different skill.)