I don't think this is the best indicator of trends. Chess players who aren't winning multiple tournaments a year, or aren't training a kid to win those tournaments, probably have very few sources of their (own) income. They'll take any sponsors that aren't dirt.

Twitch also has an entire category dedicated to live coding, so again, not all that weird to see codegen ads or something.

Ah no, the comment wasn't directed against the chess streamers! It was directed against the advertisers that choose that medium.

To take an extreme example, it would be weird to advertise Rolex on Twitch next to computer games. So, if "AI" is allegedly so desirable, why do it with vibe coding apps?

Live coding is another thing I don't understand the benefit of, but selling vibe coding to those people might make sense.

Your analogy doesn't seem to apply because AI is supposed to become an every-man thing or a utility, as are computer games, but a Rolex is supposed to be exclusive. The AI companies want everyone using AI. The Rolex company wants their brand to be associated to wealth.