It's just a side quest not related to the main story too much. These types of quests have been in the game for much longer than I can remember.
Division into smaller areas is not very popular in modern games. Most RPG have one (or several) large areas that you can move around.
Yeah, or you go open world and then vast spaces are part of the journey.
Actually if I do have a complaint about the area in Act1 is that it's very "path-y" if that makes sense. No fields to traverse or openess, it's all quite hemmed in and tunnel-esque and given that that is how I expect Underdark and cities to feel, there is an element of claustrophobicness to the map design "as things stand".
