Its to entice people to buy the full game. Just like how you have to buy CoD 2016 to get CoD 2007 Remastered. At launch, anyway.
A large bulk of their customers didn't pay for their game, the DLC is only $2 a pop, and unlike Activision, they're being open about future dates for the DLC to be standalone.
I don't see any issue with this.







