What makes you so sure? At some level of wealth, it is essentially zero effort to engage in these shenanigans; you just hire someone to do it for you. The more money you have, the higher the return on this investment. At some point it becomes deeply irrational not to do it.
Bezos and Musk think they’re saving the human race by deploying their capitol towards the pursuit of life in space.
Gates is attempting to make various diseases extinct.
Soros is attempting to bring about a world more closely aligned to the philosophical ideals that shaped his early education.
The richest of the rich usually have some pet project that they think is the most important thing in the world.
If anything, it is a much more efficient way to spend some resources. Instead of filling the bellies of thousands of red tape enabling workers, or spending that much money in pharmaceutical advertising.
The whole point of having a government is to have an institution that no one would voluntarily fund, but that we all agree to fund on the condition that everyone else does it too. It's a social mechanism designed to do an end-run around the perverse outcomes of the prisoner's dilemma. But it only works if participation is mandatory. If people are allowed to opt-out, the whole thing falls apart.