Okay, obviously a lot of the people FOR the vehicles haven't played 2, where a fully working car was introduced for your leisure. The Bethesda map however is too twisty for a vehicle.
I also kind of liked the "Surviving on your wits" way of traversing the Wasteland, it suited the sand-box that Bethesda was going for.
Why would you want to have a vehicle or mount anyway? A lot of the fun was setting a clear goal and going to it, encountering various random things across the way. Or simply wandering around a previously untouched section of map in depth. You can't do in-depth research in a vehicle or on a mount, it would be much too easy to just bypass any challenge presented. Brahmin are super slow, the Yao Gui would definitely object to being ridden, the Giant Ants now don't have a queen, so are frenzied, and all of the other creatures have even better excuses for not being ridden.