The only way to accrue value is to bring in more people who are willing to pay more money for the currency than what you paid for it.
Crypto increases or decreases in value just as any other good (or currency), based on demand, you can do Ponzi schemes with potatoes, you can’t say potates at their core are Ponzi scheme.
institutionalized fiat currency has value because the issuing country has people with guns who will drag you off to a metal box if you don’t use the currency in the intended ways (unless you’re super rich I guess).
And cypto’s value is that it’s a currency outside the (at least the digital) reach of a countries institutions. No institution can give an order to block your transactions! Even if you’re bank account is blocked, you can still trade with crypto! That’s at least one of the reasons it has value!