The way I've been thinking about it: there is too much money trying to pour into the market. That's why valuations are so high. Maybe getting more of these big private companies public will bring valuations down a bit. (Just my impression. No math or financial studies behind it :)
No, the crash (that we all know is coming) will do that. Until then, history teaches that we'll just keep going up and up
Stock prices don't have to crash. They can just stagnate while profits catch up and multiples compress.
Debt binges, on the other hand, tend to go bust with a bang. But after the recent private-credit scare, the AI build-out has been predominantly financed with stock. (I think.)