They're providing an after-sale service for another user, though. It's not about the disc, it's about the post-sale services. The more times a game gets passed around, the more expensive it is to provide online services vs a single person buying and holding onto a game (on average).
They're providing you a service at a certain level of cost and they weren't party to your purchase of the game at all. So they want to reintroduce themselves to the relationship with this thing, make some money off you, ostensibly in exchange for lifetime online services for that game. If you don't want online - just the game on the disc that indeed isn't costing them more - then you don't have to pay anything more.