There is also a real reason for it not to be done with NFTs: it would take about thirty seconds for someone to be scammed and open a support ticket with [whoever - it won't be the right person, but I guarantee someone is getting a support ticket] and they obviously won't be able to reverse the transaction, and also unclear if they could even ban the scammer (right now, bans are per-server, unless server owners have coordinated otherwise, which they generally don't). Regardless, the user is going to have a bad time, versus a system using a mutable system, where a human could investigate and reverse the issue.

Obviously support agents make mistakes sometimes too, but that's a heck of a lot rarer than scams in MMOs.