Being a game developer isn't easy. You live at the whim of your publisher and even great games can flounder and drown. If you're lucky people will like one of your games and then you get to churn out sequel after sequal because that's what the publisher will pay you for.
I sometimes wonder what a Trokia KotOR 2 would look like.
That said, as someone who liked Morrowind, I thought Oblivion was a horrible, boring and unfun game. If it can make money (and it did) Fallout 3 can make money.
Lucas Arts wouldn't have liked it since it would most likely get a M rating. Seeing that their past games, Troika and when the developers were with BIS, had sex, drugs, foul language and gory blood, I don't think LA would have given them a thought.