I can’t find it on GOG’s but I wouldn’t be surprised if it’s in most EULAs. I’ve seen emails saying “confidential, if you are not the intended recipient of this email you must delete it.” There’s no way to enforce that. Ubisoft isn’t coming to your house to review the contents of your drives. I’m guessing it’s to stop some loophole like “you said I can’t resell your game so instead I sold my hard drive (that has the game installed on it)”.