Besides, an additional reason could be that the Vault Dweller as of his memoirs was pretty distraught and had lost all his companions and friends, and those places that weren't connected to them he wasn't a huge fan of (Junktown, the Boneyard etc) so he would just want to put his arduous journey behind him for good. Why did the Vault Dweller explore anywhere on the map that wasn't absolutely necessary in Fallout 1 to his quest? Why did he do anything but the most necessary objective? Because he's the kind of person who would do that, explore unknown territories.
Why not? Human beings are not always utility maximizers that make the most optimal decisions, they oftentimes make decisions for arbitrary or irrational personal reasons. >why did the vault dweller go far into the north?
