They're saying that he didn't start a billionaire. He multiplied his wealth by a factor of a thousand or more.
The ways one can use to multiply millions by a thousand aren't open to people that only owns thousands. And you really don't want to multiply your possessions by a thousand if they are negative.
Simply because if you've such wealth already you're most likely in a position to take risks, etc.
A billion is actually just a lot of money, there's a much more finite amount of room at the top.
All you need to do to make a million quid in the UK is get a 75th percentile job and save half of it. After a few decades you are now a millionaire. I mean, everyone can't do it, but it's not some unfathomable task.
In the US I imagine it's even easier. Your median income is lower but the top end is insane.
I agree that it is possible, but it is sadly an impossible task for most. That's my point above: for those who have wealth it is easy to grow it. It takes money to make money.
My other point was that those who have a billion started with millions.
I might be misinterpreting the facts but Gates got the deal to sell DOS to IBM because his Mom knew someone or was on the board. Bezos went from a successful career in finance to start Amazon. Zuckerberg started Facebook at -Harvard- and partly, the success of Facebook was predicated on Harvard's social prestige.
I just don't understand where people come up with these weird bootstrap narratives from.