Musk, Bezos, and Gates would have access to all of the funding in the world for any future ventures. What the government could do is lower taxes on everyone else.
I have not seen a single wealth tax proposal suggest the funds be used to lower taxes for others, and it's incredibly disingenuous to suggest any wealth tax proponents want to do that. These types of tax proposals are always to fund other services.
How's it disingenuous to propose that the government could do something with a wealth tax besides spending it on social programs? If we're talking about what leftist politicians would want to do with the money, then we shouldn't be talking about a wealth tax at all, because it's likely never going to ever pass a national scale.
It's disingenuous to propose it as a viable option when every proposal involves spending the money on something. These things do not happen in a vacuum.
Who are these proposals coming from and what kind of traction do they have with voters? My answer to that is they are coming from politicians rallying their base for primary elections, knowing full well that the proposals are extremely unlikely to come into fruition.
I am suggesting something that might actually get the middle class, or those aspiring to join the middle class, to support and vote for the idea. I think it's pointless to talk about more radical concepts like a wealth tax or UBI without considering how such a thing could be made appealing to a majority of voters.