Empty-nesting has been a thing for about 2-3 generations. Before that there were often multi-generation homes. But it seems like people didn't really up-size 2-3 generations ago. Many of the great generation were happy to build their 1000sqft Sears house and live there the rest of their lives. The last 1-2 generations seems to be more of a drive for trading up to bigger and better everything. Now we see empty-nesters in 2500sqft houses. I think it's natural to not not want to leave a long-time home, even if it is oversized and only filled on holidays for company or parties. But why do we really need that much space in the first place, seems to be more of the question.