You can be pretty sure that they have legalese in the eula that says that your right to use the software expires with non-use.

It's not even in legalese. I'm on my phone right now and thus have no motivation to look through a couple EULAs but I did read the interesting parts of a handful of software EULAs. A couple straight up state that they can revoke your access for any reason (usually followed by "including x, y, z"). And especially for multiplayer games, I understand why you would prefer your wording as such instead of having to list and define every "bad behaviour" like cheating, cracking the game, being an asshole to the community (including the moderators), etc.

The decision makers at Ubisoft, I imagine, just went ahead and said "How about we take this 'for any reason' to the absurd? If just 1% of the deleted accounts is remade and buys their games again, we make a lot of free money."