You have it backwards.

Only if you can prove that there is not a person with access to the account and intention to access it can the account be deleted.

This proof is technically impossible and thus does not make sense as a solution. We are living in the world where zero trust is default and bad things happen, so the ONLY right way to protect customer data is to verify the identity regularly, rather than declaring it valid once and forever until proven otherwise.

We aren't living in this world, that's your imagination. Rather than making the users suffer by default, identify a more specific "bad thing" and address only that with the min user inconvenience

Dude... come off it.

You're wrong here, both legally and technically (and in my opinion, also ethically).

In the bluntest possible way, even if you were correct (and you're not...): They could have just deleted the billing information and not the account.

Ubisoft designed products that require an online account to use - Ubisoft is on the hook for providing that online access for account holders because they paid for that product. Alternatively - in any region with good consumer protection laws, they're about to issue a lot of full refunds.

A digital purchase is often the purchase of a license to download and execute the product. If that's the contract, then it is necessary to keep some PI on file in order to respect the terms of the contract: offer a download upon request to a particular person. No need to keep PI on file indefinitely: the purchaser is enabled to take their wares and the store to remove accounts if dealing with PI laws is too much hassle.

If this is too much hassle, they could instead sell a license to execute the software, regardless of how it is obtained (but offering a way to download for now, putting the purchaser in charge of backing up those files). Similar to what GOG are doing.

But no, that's not enough control for them either. They want to have their cake and eat it too.