Your not understanding. The concept of the game is that the player can get over ANY geometry. Yes you can use mountains to block players but for one the entirety of skyrim would have to be encircled by mountains which is both stupid and doesn't follow the lore of the world.
On top of that a main draw of the game is that you can traverse to the top of any mountain and go anywhere.
So yeah it would have kind of ruined that.
"You can travel to the top of any mountain!....except all of the ones surrounding skyrim..."





OT ALOT ALOT ALOT ALOY {ALOY?} ALOT 

This^