They could be considered a transaction tax and/or payment processing fee. But they are not the reason people would be willing to accept a token in exchange for

They could be considered a transaction tax and/or payment processing fee. But they are not the reason people would be willing to accept a token in exchange for some real resource like labour, because unless you’re already using that token you are not obliged to pay for anything using that token. Demand for that token is thus entirely speculative and could evaporate at any time. Since there is no issuing authority that guarantees to accept the token in order to exonerate some obligation we have in common the last person holding the token simply loses the game.