Not all financial scams are Ponzi schemes. Most are not. Ponzi schemes involve the operator deceptively using incoming funds to pay out early investors. Ponzi schemes are based on deceptive manipulation of cash flow not on price appreciation.
If Bitcoin were an actual scam (and I'm not saying it is is) it would be a pump-and-dump. Most ICOs and shit-coins are clear pump-and-dumps.
There is a huge variety of financial scams, and it would be a fiscally safer world if more people knew about them and could discuss them.