Why do I keep seeing there's not enough BTC for every millionaire on Earth?

There's over 50 million millionaires in the world. I've read over and over again that there's not enough BTC (21 million) for each one.

Is this some enduring fable that people just repeat without questioning?

Edit: I think I had a stroke (kidding).

I'm going to leave the post up just to watch myself get dragged online by strangers.