Well Bungie signed a contract with Activision. In that contract would have been language about who gets final say as to what gets cut and what doesn't, DLC management, etc. It's one of two ways: Either Bungie entered into a contract with Activision and gave too much away as far as creative control, or (more likely) Bungie is doing exactly what they wanted to make more money with a mega-publisher like Activision. It's just how the business world works.

Bungie makes the game... Activision deals with everything else; the cut out content... Prices is all Activision.