I think that is a really bad line of logic. There are lots of things that have been around for a long time and make some people plenty of money that are bad things. Pyramid schemes fit your definition - should I start buying in?

The opposite way to pose this is: Cryptocurrencies have been around for 9+ years, and there has been literally 0 use for it apart from conning rubes on the internet. The important thing to ask is whether it has a purpose and has it delivered on that purpose. There's really only one theoretical purpose that it's meant to serve - being free from tyrannical government. Well that kind of worked when capital fled into it from China - but there's also been crack downs. It also doesn't explain the US fascination.

I think there comes a point where 9 years in, you have to ask: What purpose does cryptocurrency serve beyond enriching people who are already invested.