alt Hacker NewsBanks don't just keep your money in a vault when you store it in a bank account - that would be stupid both of both the bank and of you. Money looses value over time due to inflation, so banks reinvest 90% of your stored balance into loans, stocks, bonds, etc. This means that a theoretical 1B account, would allow someone else to take a 100M loan to fund a new venture. This is how banks make money, and they pay you a small portion of their profits as interest on your money (since they're profiting off it).
This is still not a good idea for you, as the interest doesn't make up for inflation. Most people keep a small portion of their wealth in the bank, as easy access for emergencies (this is called dry powder[0]). The rest is typically invested into private equity, which allows new ventures to be created.
It's very rare for anyone to have more than $50m in the bank. The money is usually out in the market doing it's work.
The point of the story really was that most rich people, those who don't work for a living but live off of capital assets are in a position of economic power where their wealth accumulates. When the real economy grows a few percent per year but the wealthy gain 10-20% every year their wealth comes at the expense of everyone else.
This is the trickle up economy where the few people at the top suction all the wealth to themselves. And the rate at which they acquire it exceeds the rate at which they spend it.