They should.

Because if you invest, you'll be in queue to get paid. You have to wait for some time or forever for you to get your turn to double.

When you invest, the top dude on the list will get paid. They're taking your money and giving it to someone else for them to double, after charging some fee.

They're not paying anything out of their pocket or business. If you're interested, don't invest more than you can afford to lose.