It certainly is silly, what incentive does a game developer have to let someone transfer in game assets they bought for a different game instead of selling the in game assets themselves? There isn’t any incentive to allow it so it won’t happen.
If you mean transferable as in able to sell an in game asset to another player, Valve has offered that for at least a decade.
Yep, it's the same reason why I can only smirk when people tell me that crypto is the next thing for buying/selling "used" video games. News flash: The reason why you can't sell your games on Steam isnt because of tech issues...
The earliest popular instance of this model I’m aware of is Magic: Online, which went live in 2002 and worked entirely on physical analogy. You would buy virtual card packs just as you would physically, and could trade cards between players without restriction. This was seen as an evil ploy by many at the time, who balked at the idea of it not just being a subscription model with unlimited access to cards.
Purchasable is also (usually) silly, but here we are.