Investors, mostly private - eg. SoftBank and all the other deep pockets funneling money into this - but also public, because lots of people are invested in Nvidia, Microsoft, and Google, who will be directly affected if the bubble bursts, and just everyone invested in the markets generally, as this bubble bursting would already probably be more broadly damaging than even the dot com bust was.

Personally, I do expect a big correction at some point, even if it never reaches the point of bubble bursting. But I have no idea when I expect it to happen, so this isn't, like, an investable thesis.