But Obsidian could have made any narrative hook they wanted, ideally one not in contradiction to the game they were creating. That’s what I don’t get.

Though it is a little overplayed, having a mystery to solve affords the player a lot of latitude to explore the world without feeling like they are just ignoring the super important, crucially pressing, imminent danger that would work much better in a more linear game. At least Dragon Age: Origins gave you a valid reason for visiting every corner of the map petitioning for help and solving everyone’s problems. As it is, the main thrust of the plot is completely divorced from the rest of the game. It’s very odd.