When you hit a hundred billion in net worth, you get a nice solid gold plaque that says "I won capitalism", you get an attaboy from the UN, and we start taxing the shit out of wealth over that cap.
Adjust periodically for inflation. (Do that for minimum wage while we're at it.)
It's because while for some people there may be jealousy involved, many more have realized or are now realizing how much power the ultra rich have, and how bad that is for our societies.
Once a company becomes large enough, it becomes so influential in society that control of it must be made more democratic.
I don't think anywhere has figured out quite the right way to go about it yet, but it's clearly the right goal. Some countries require employee representation on the boards of large companies.
I find these special founder-class shares that completely insulate folks like Musk and Zuck from their actual investors to be deeply problematic.