FO3 + NV have massive replayability, especially when combined with mods. People played those games over and over again, role playing totally different characters.
Your gut-feeling about Bethesda games lacking replay value is at odds with objective stats. Skyrim is even still in the top 10 played games today on Steam 5 years after release (and was a stubborn fixture in the top 10 even before the remaster)[1]. Fallout 3 + NV stayed there for years. Admittedly, FO4 dropped out quicker than usual, but a lot of people blame the constricting nature of a voiced protagonist. FO4 is nevertheless still in the top 20 for most players today a year after release.
So their games have definitely got replay value, they really get replay value. Their worlds are full of unique locations. I do admit they got something a bit wrong with FO4, but I think even they must realise that at this point given the player feedback.