I'm not sure what point you guys are trying to make here.
They *choose* to tell a story that spreads across several different regions, they don't *have* to.
They could pick a single small town, its surrounding area and according to what level of detail and amount of content they want to pack in it they still could have the tools to make a game which is twice the size and length of TW3.
This is a continuation story, and the CDPR has probably chosen the best possible places for it to take place and makes sense. They could have not created skellige and map would be 1 huge area(novigrad and NML) but important characters of this story have roots in Skellige which is also home to many other and it is a good change of scenery with more nordic themes to diversify the game. Or they could have discarded Novigrad and NML and just made Skellige more bigger then we would miss big cities, much of the ongoing war and many other things. I'm assuming here, probably CDPR has more or different reasons. In the end we have both. So yes, they chose this and I think it's a choice to make the story great.
They are not trying the fit the story into a limited area, they try to fit regions for the story. <this could have been better with different words, unfortunately I'm not capable