They are, though, by any reasonable definition. Despite what the cryptobros would have you believe, there is no need for a blockchain to have a tradable, persistent token associated to an asset. Besides the fact that the tokens are stored on Valve's servers instead of a distributed blockchain, there is no difference in how those work.
The cryptobros tried to convince everybody that a blockchain made the tokens "non-fungible" as in automatically interoperable and endlessly persistent, which was a lie that only survived until the first time the assets, which were all stored on servers and not in a blockchain, got deleted.
That's a different discussion in any case. The point is it's a stock market of tokenized, tradable items where the transactions are monetized by the company by taxing the trades. It's the same on Roblox and Steam (and in all the NFTs people dumped all that money on).