There've been a _few_ of these over the last decade; _two_ attempts at blockchain stuff (an initial "use blockchains for everything" one, and a "use NFTs for everything" one a couple years after the first crashed and burned. And then of course there was 'metaverse'.
VCs just need to make sure there is enough hype by the time AI startups IPO, so that they can cash out. It's part of a bigger trend in finance, arguably caused by quantitative easing. It's why Uber could IPO, while they had never made a profit; but because of the hype, their stock price did great on day 1.
I think this hits the nail on the head. At least, it's the only explanation I've heard that makes any sense.