That's exactly it: you may wish it, but the reason it won't happen isn't that NFTs weren't invented yet, it's that companies making these products really don't want you to. One simple reason is that it might make someone else play less if they could all those items by just paying a little money.
The other reason why selling in-game items for real money will never be permitted (again) is all the gigantic legal crap that it brings along. If the items are worth real money, you can sue Blizzard or other players for events which unfairly make you lose an item, or affect the value of the items you hold.