The idea that the rest of humanity needs to support them is absurd. A couple billion in private trust funds could fund mathematics researchers in perpetuity.
The idea that "someone rich will take care of it", reminds me of a passage from https://en.wikipedia.org/wiki/The_Logic_of_Collective_Action. It talks about "the exploitation of the large, by the small". Where a public good (in this case mathematics) is provisioned by a large entity that finds it worthwhile for their own reasons, and the remaining players who value it, feel no need to contribute anything themselves.
People unaffiliated with the Linux foundation contribute to Linux. Regularly.
Supporting a group of elite mathematicians is not enough. There needs to be a path to becoming an elite mathematician.
Which either means that it becomes an unpaid hobby. Or there is some wider source of support for the profession.