If you put that $50 million in that same fixed rate investment you'd be getting $2.5 million a year. But wait, we want to keep up with inflation! Let's assume 3% inflation year over year. Your leftover 2% to live on is a measly salary of the equivalent of a million dollars a year growing with (historically standard) inflation.

To the ultra wealthy that's not much, and you certainly aren't living like a greater member of the House of Saud or buying everything you could possibly want off of it, but you can live a life of great comfort, travel every year, have a nice home, have plenty of comfort and hobbies, and never work.

And to get back to this, this is an amount of money a billionaire can give someone every year without touching the principal. If the billionaire wants to continue growing with inflation it reduces to them getting 20 million a year which translates to 400 thousand a year both matching 3% inflation. That's still a comfortable life in even very high cost of living cities.