In most cryptocurrency schemes, there's no financial activity other than investors buying in and cashing out.
There's literally no way for the thing to make money.
If I invest in a mine or a retail store, there is a way for the mine or retail store to generate a profit and pay off my investment (with interest).
Crypto crap is all about inventing new take money tokens and hoping nobody looks at any of the details.
Maybe exchange fees are a small way to make a profit from facilitating illegal activity, but I would be surprised if the return on that is even OK.