Good point - I wondered about this too, since it's pretty easy to see any obstacles/enemies so nothing can surprise you. Didn't bother me too much though, even though it does somewhat diminish the exploration/danger aspect. Some areas are quite large, so at least this way it's easier to plan where to go.

I realise the old Fallouts definitely did have FOW, so it's kind of strange that there's not an option for it here at least...

You'll still need to actually go there to look at stuff and grab loot though. Also the loot highlight key has a limited range I think. So it's likely a design decision.