RPGs are extremely popular and they sell extremely well, and I have to tell you now. Games like Fallout 4 were about as mainstream as you could get. I mean you could argue that Fallout when it originally came out was a bit of a niche game, mostly because not that many people knew about it's existence. Although even then I'd say it was reasonably popular. Fallout 3 changed that, it kinda made it a little more mainstream a little better known.
But by the time Fallout 4 came out, Fallout may well have been one of the most well known franchise expected series that has ever been out.
As RPGs go Fallout had become so mainstream everybody knew about it. It was the epitomy of tripple-a mainstreamyness they didn't need to make it any more mainstream for "RPG gamers". It wasn't too complicated or too niche for "RPG gamers".
And if your argument is, well they tried to make it a shooter because they thought they could sell more as a shooter than as an RPG. I want to know where you're getting your figures from, and why you think trying to sell something everybody's expecting an RPG from is going to do better if you make it into a shooter. I don't see the logic behind that.
All they had to do to make this game sell was make it a Fallout game, and the expectations from the previous games; Fallout 3, Fallout New Vegas and even Skyrim would make the game sell. So I don't buy any of these arguments. They did not have to dumb anything down, they did not have to change the genre from RPG to shooter. They did not have to do anything to make this game sell, beyond making it a Fallout game.
A far more logical argument is they made these changes because they thought people would like them more. They listened to the criticisms people had been throwing at all their games; Elder Scrolls and Fallout. And they tried to address them.
