It's tied to everyone's retirement being automatically invested into it. I wonder what it would take for a bunch of white collar workers to cash out their 401k early.

It's tied to GPUs. Nvidia accounts for ~8% of the S&P 500 as of this comment.

AI is propping up the US economy - https://news.ycombinator.com/item?id=44802916 - August 2025 (439 comments)

They're definitely fueling a bubble but the S&P500 was already bonkers before the AI craze.