If the charity itself is doing proper work, that makes sense tbh. I mean, if you had billions to donate, would you give it to some random ass organisation... Or set up your own thing to do things that you personally agree with?
Honestly, I’d go for the middle option: donate to existing charities that appeal to me. I don’t want to run a charity, it sounds like a massive headache.
You’re probably a different demographic. I’d guess the kind of people that become billionaires, assuming they actually want to be philanthropic, think that they can do a better job of managing their charities than existing charities would do managing their donations.