Not sure this had been brought here but it looks like you don"t really "rest where you are".
It looks like you're teleported to a specific area that doesn't exist anywhere on the map (like the main camp) but with an environment that fit your previous location.
Well, they haven't been exactly secretive about this. Their explanation made it clear enough, I would say.
From what I understand, they HAD to make a specific camp area for each world setting, because otherwise if you just dropped a campfire in the middle of wherever you're standing (which could be on a narrow bridge in the Underdark for example!), in cutscenes you might have characters walking through walls or on air, etc. Also imagine the lighting issues - world lighting vs specific cutscene lighting, light being affected by colours in your immediate environment, etc. This makes sense. Also from an RP perspective, you wouldn't just make camp wherever, you'd look for somewhere secure and out of the way of predators/enemies.
Sort of.
First things first, even other games that allow you to "drop the camp wherever you are" like Kingmaker and WotR actually limit the options to areas where there's enough room to actually place one. It's not like you can "glitch" a temporary camp over any geometry with complete disregard for anything else.
And of course in these games you'd need to be at a minimum distance from enemies, too.
That aside, frankly I don't think that the trick of having "contextual cutscenes" with variable background (which it has already been used by plenty of other games before, for the record) would have been particularly harder to adapt to "contextual camps". I think it was just a deliberate choice from Larian to have these camps instanced.
