Some games are designed with a certain Aesthetic in mind. The developer chooses it, and they run with it, and build around it. I'm not a fan of the isometic view much anymore, but that's not to say it shouldn't be a thing anymore.
A lot of games use it, and use it really well.
It doesn't really work with the modern fallout, because then you would miss all those neat little graphical details Bethesda does because the camera is WAAAYYYY up there rather than where you can fully appreciate them. Not to mention playing "find the pixel" with smaller items you could pick up in the world, and lordy all the containers in that view...
Not to mention, the settlement feature in isometric view would be horrendous in isometric.