You're right, you don't need an immutable ledger of visible IP licensing rights if that's all you want to accomplish.

But presumably, in a "legal piracy is commonplace, Steam goes out of business" scenario, the studios producing the games would still want to make the games verify your license ownership against something — e.g. to make sure that you're only using your license for one concurrent "seat", rather than using it to activate thousands of copies of the game (like a regular product keys — which usually are "local digital signatures" — would enable.)

Presuming that no central corporate authority could 1. profitably exist in such a market 2. with the right incentives, then a distributed immutable ledger would be a good alternative for storing those licenses in a verifiable manner. (Think of it as an IP licensing activation server run by "everybody." Each time a game wants to run, it would use your signing key to submit a TX incrementing a counter representing the current active uses of the license. Basically, a distributed, cryptographically-verifiable semaphore.)

Perhaps, but since the premise of the solution is that Ubisoft must be legally required to provide a certain service to the current bearer of the token, then it seems overkill to put this on a distributed database system with a complicated consensus model. If Ubisoft is already legally required to recognize it, then surely they can also be required to host a service for moving ownership or maintaining a usage counter in a publicly verifiable manner. Still, NFTs are not the solution here.

Legally obligating each studio to run a centralized service for license verification would be no better than requiring the publishers/distributors to run such license-verification services; in both cases, the backends would die with the economic actor.

The nice thing about an NFT (per se, a deed), is that you still own it, and it still has legal effect, even after the entity that originally created it ceases to exist. A distributed ledger will remember that Ubisoft granted you an IP license for X, even after Ubisoft stops existing as such, with all their assets sold off or lost. And any games built to check that distributed ledger, will continue to find your license there, and start up just fine.

But those games are running on hardware that you control. You therefore also control what version of the ledger the games can observe, and you can choose to show it an old version or a fork that has been mined with a tiny amount of PoW, so things like activation counters wouldn't actually give you the guarantees you are claiming. Perhaps for online gaming, the peers could require proof of ownership via the central ledger. But I would imagine that everyone would just apply a crack to disable those checks, because spending crypto fees whenever you join a server just to protect the IP rights of a defunct company is such an overkill solution, and frankly I find the use case highly contrived. I don't think it is realistic to assume that gamers will accept that what used to be a simple license check now involves downloading and verifying gigabytes of ledger history.

Just use off-ledger verifiable receipts. If Ubisoft goes under and sells off its IP, then the buyer should be legally obliged to run a similar ownership service with the digital receipt being the proof of ownership OR release the games to public domain without license checks.