This line of thinking always makes me laugh. You don't complain when a doctors makes money by serving hundreds of patients every month right? Then, when someone builds a product/service that is used by hundreds of millions, or billions of people, the natural conclusion is that they will become millionaires and billionaires.
It's very natural, and very logical.
> we are talking about people who control more assets than some nation
How about folks who centralize powers like politicians in high level functions, who have not even been elected but appointed? How do you feel about that? They also can have massive influence on the world's affairs, even if they are not billionaires. I'd be way more concerned about that.