Ponzis prey on greedy, foolish people - some of whom actually believe the lies being promoted about it being a real investment. It's even worse in the cryptocurrency world, where fools are convinced that they are buying shares in mining operations or super-secret trading bots.
These games should really be considered simulated bubbles instead of Ponzis. A Ponzi scheme collapses when the operator walks away with everyone's money. PoWH3D doesn't have an operator since it's totally decentralized. It will collapse when everyone decides to sell. Likewise, CryptoCelebrities will never crash but inevitably somebody will get stuck with a collectible that nobody else wants to buy. It's akin to buying a beanie baby or a tulip for an exorbitant price, only to find that there's nobody to resell it to.