The game totaly lack of (side) quests or story elements that gives us goal to explore most of the map.
Is this even fair to say, since you have that situation conditioned by ignoring one companion, and one vendor? O_o
If only 2 characters gives narrative reasons to explore 25% of the map, yes I think it is fair to say.
It would not hard to add story reasons and quests as there are already great content in these parts of the map arround which new short stories could be created / reworked a bit to make them a lot less hidden (shadow druid, burning inn, gnolls on the road,...).
Not saying that there should be reasons for every small areas though. In exemple I personnally don't have big issues with the lost chapel as we can't really miss the locked door down and the looters on the top...
A dungeon and people fighting to keep the loot is a good enough reasons to me... but yes I'd also like to have narrative purpose to explore what could be considered as "side parts of the map" no matter my companion and main story choices.
