Depends on the country. There are places with "mountains next to open grass lands next to coastline next to forests within a few miles of each other" (where few, eg. 100 miles). The world is not all like Utah US50 or whatever huge expanse.
But even so,
(1) there's something exciting on its own for driving in real-mapped as opposed to some fake designed terrain
(2) for certain games, it can main point (e.g. I can imagine a "route 66 hot rod race" or a "drive Monaco Rally" (and of course things like MS Flight Simulator, combat games, etc)
(3) There's absolutely no reason why a game couldn't use real world data and cherry pick different terrains for variability from those...