The thing is though that in those games like Wolfenstein and Dishonored it has a very clear and thought out story and good gunplay, essentially it is meant to be play on it's own and vanilla, but the price of having a overall better story and game play is the very linear story, which reduces replayability of the game as well as the longevity, so it is a really good game... For a single playthrough. after that though their is very little incentive to go back. FO and Elder scrolls on the other hand are built to have a pretty shallow story and basic game play as a price for a whole lot of freedom and role playing ability. It wants you to try and make your own story. And very many people achieve this through tweaking their game themselves or looking at what others have done, aka mods. So it is actually not too inaccurate to consider games like FO and Skyrim "sandboxes" in the sense that they are actual built to be molded by the player, where as dishonored and wolfenstein are meant to be play like any other game is, by the "rules" put in place by the developer.
Holy [censored] I had no [censored] idea I could explain something so well and in so much detail.