The Capital Wasteland doesn't suffer so much from invisible walls, but the Mojave is different. I've heard so many reasons as to why there are invisible walls, but it doesn't matter why. Most times they're annoying.
In certain places, invisible walls are needed. Places like Repconn Test Site cause problems with collisions involving much of the buildings and scenery. More often than not though, you're just trying to climb over a dividing wall and get to the other side. You'll often get on the ledge or on level ground, but you can't proceed further.
there are mods that remove invisible walls, but that gets hectic. If there aren't any mods that remove ones that have no reason to be there, how would you guys feel about a TTW friendly mod?