So would it be better if they actually made you download the stuff? I mean your whole point is that the data is on the disc and you shouldn't pay for stuff on the disc, but what if they never put it on there and made you actually download the thing.
It's moreso their motivation for doing so. Usually extra content is something released after a game is, because developers needed more time to work on it, or its something fans wrote in about, or whatever. So they add it as DLC and slap a price on it. This, however, shows that they had already made the content when they had finished the game, and merely though "hey, we should not let them have this part of the game for free, and instead offer to unlock it for a price".
You can speculate about what kind of DLC you will have for your product, but when you have it ready as the product is ready, thats pretty shady, like it would be part of the game till someone decided enough people would pay money for it. And having it ON the product, just not accessible for free? That's flat out admitting it.