There are only a few cryptocurrencies that have any significant adoption, and fungibility is fundamental to that value. If I exchange a bitcoin for $N, that validates the value of all the other bitcoins. And folks exchange large numbers of bitcoins for $N every day.

By definition, every non-fungible token is its own unique snowflake. There are new snowflakes made every day. Few ever trade, and the ones that do are probably wash trades.