To me, the camp system is a way for you to switch out party members if you get stuck in a dungeon and need to swap out say, a rogue for a cleric to continue past a certain point. I hate it and think it's clumsy, but that's my guess as to why it exists. Dragon Age also did it so maybe they took inspiration from that?
For the interface issues, if you look at some of their past articles on DOS:2, the current inventory interface looks almost exactly like what they wanted to do for a controller / console interface. I don't think that explains why you can't flip between characters or have a shared inventory (and weight limit), but to me their desire to appeal to both controllers and kb + mouse players is a cause of a lot of the interface issues.
