when it comes to hearthstone blizzard decides. you can have every single nft on the planet, but if blizzard decides you dont get to use those cards in hearthstone you 100 percent absolutely don't get to use those cards in hearthstone.
NFTs are just as useless. I can sell you the NFT for the original doge Shiba Inu, and I can sell Bill the actual legal rights to use that photograph.
Despite you owning the NFT, you can't actually use that photograph. Bill can. And he can sue you, and win, if you try to.
All that ownership of the NFT entitles you to is... Ownership of the NFT. It's like owning a photograph of the deed to my house. It doesn't mean that you actually own my house. You can keep reselling that photograph, but it's not going to get you any closer to owning the house.
But eh, we can burn a lot of electricity to certify that you do, in fact, own that particular photograph of the deed. Fantastic. Meanwhile, I can take, and sell more photographs...
In this situation, the NFT does come with usage rights (like a license) and isn’t the same as selling a picture of your house.
The only benefit is having a 'public' API for ownership of an item that other, third-party games could use, but why, as a game developer, would you possibly give any rando third-party competitor full access to this information? It makes sense if you are curating a community of fan-made tooling that ends up promoting your game, but it makes zero sense to give competitors access to it.
Imagine a Hearthstone-clone that pitches it as: "Join our game! You have every card that you own in Hearthstone! And a <gimmick>."
Do you think it would be in Blizzard's interest for that clone to exist? Do you think it would be in Blizzard's interest to go out of its way to turn its player's cards into NFTs, so that some unlicensed Martian knock-off goes ahead and makes that pitch?
It is in Blizzard's interest to share this information with someone that they have a partnership with (or with another game that they've developed), but that problem can be solved by... An API. With revocable keys.
Some NFTs are extremely valuable (e.g. Crypto Punks) and attract many clones. The clones may be on the same blockchain and have very similar or even identical art. Or, the clones may reuse the same art but issue tokens on a different blockchain. In all these cases, the social consensus on the value of these clones is approximately $0. It's a weird psychology.