I'm not following your logic at all. I don't think it's a common phenomenon for retirees who once lived in urban or suburban areas to move to rural ones. I'm guessing the majority of these people have always lived in rural areas and just stayed put through retirement.
That doesn't matter--the point is that because retired people don't need to be near urban jobs, we can reduce pressure for housing in urban areas by leaving retired rural people where they are. (Or, conversely, we can avoid increasing pressure for housing in urban areas by moving retired rural people into urban areas.)
