It ties in with the idea of the American Dream: anyone, if they are willing to work hard enough, can be rich. So, logically, if you are not rich, you are just not trying hard enough.

So people grind and they grind and they grind and they grind, then collapse in exhaustion, and then they think. Then they turn to their gullible neighbour and say, "Hey, you're not rich. Let me show you how to become rich. You'll need to invest in yourself by paying me first, though."