And most importantly of all, game publishers do not want you to be able to use something you buy in Game A to decorate your character in Game B, because they want to skim more money out of you buying a new artificially scarce item in Game B.

Hell, Valve literally already did this with all CS:GO skins carrying over to CS2, it required zero blockchain, doesn't actually give you "control" over the item, and was only done because players have spent literal tens of thousands of dollars on skins and Valve needed to throw them a bone so they would be slightly less upset about CS:GO being essentially memory-holed.