It's possible they used an off-the-shelf solution or something built by another team within the company and didn't think much about integration. However, that is completely irrelevant from users' point of view.
However, like
@RejZoR said above, if users rage about this and then turn around and buy Bungie's next title, I have no sympathy for them either.
Edit: And about developers, they always get lost in their own space. It's inevitable when you do the same thing over and over and over and over again. That's why there's an architect somewhere and that's why, imho, the dev team should never sign off on anything. QA should.