There aren't that many billionaires. The Wikipedia article on them says that there are only a bit above 900 in the U.S. and a little over 3,000 in the entire world. They have a lot of money, but only because other people voluntarily gave it to them because they valued what they were selling. Maybe this isn't the case worldwide and I'm sure there's a warlord or two that managed to export enough wealth from the people to be considered a billionaire, but most of them got there because they built something valuable, perhaps a few because their father did.
I don't entirely blame the problems of the present on previous generations either. They certainly could make life better for the current or next generation, but why should they. Many of them worked hard to get where they were. Many more worked hard and got nowhere. Why should they give up what they earned to spoil someone who lacks the context to even understand how appreciative they should be. They'll be dead in time and their assets will be passed along regardless of whether they hoard them right now.
If you want to blame someone for the world not turning out the way you wanted it to, look no further than the mirror. Why don't you amass the wealth or power to shape the world as you wanted it to look? Why would you expect anyone else to do it for you?