They aren't using randomly generated dungeons or anything, they have to place every asset by hand. Given that the atmospheric storytelling is one of Bethesda's strengths, and the new area is supposed to be bigger than Boston, I just don't see the problem. Heck, I'd go so far as to say they created too many assets for Fallout 4 NOT to reuse them in future titles. It's not like I ever ran out of weird places to explore in that game, it was massive. I found myself more fatigued at having too much to do than anything else.