Because I've come to terms with how these things work. That's how a lot of AAA publishers set up their budgeting now (part for the main game, part for the DLC), and I know being an internet warrior about it honestly isn't going to do anything. As long as the base game is good, and has a good amount of content, I don't have an issue with them making DLC at the same time as the base game.
In the end, yes, there's plenty to argue and debate, but it comes down to a simple choice: buy or don't buy, or in other words, support or don't support. If you're so passionate about it, skip the vanilla edition and buy the "complete" collection later or just boycott the game in general.