Consider the effort to reward curve though.
Unlike the hardcoe fans on the forums, most people do not beat a game multiple times, they play through it once, twice if it's good.
Lets say you have 30 "work units" of quest you can design. Each unit represents both programmer time, voice acting budget, art budget, every resource that has to be consumed to make a game, it's not just a man-hours measurement, it also represents budget and testing time required and the increasing probability of bugs the more complex a game gets.
You could make one 24-unit long main chain with 2-unit differences (rather minor) for the three sides you can choose, lets assume a unit takes about 1-2 hours to play through depending on how grindy it is and how high you slew the difficulty curve, that's three slightly different factions and a game that most people will get at least 30 hours of gameplay out of it.
Or you can make 3 totally unique paths each 10 units long and have a game most people will only enjoy for 10-15 hours, then go online, complain it isn't long enough and they got ripped off.
Totally divergent storylines really are terrible from a design standpoint, since most people aren't going to replay a game that many times unless they're already hardcoe fans.
Not saying that you're lying but I don't believe that they couldn't have created long unique quest paths.
And for the "most people will only play through it once", well, isn't that their own fault?
As I said, I feel like they didn't give the full truth about it pre-release when they were hyping it.
"You can choose to join Legion, NCR, House or be independent", yeah, that's true, but it's a vague truth.
They didn't bother saying "Oh by the way, no matter which one you choose the quests will be the same."
It's more than any earlier game did for us that's for sure so it is a step forward, but it wasn't even remotely what I expected.
But that doesn't mean the game is bad.
It's a step forward.
Even though it's just a tiny tiny tiny step.