One thing no one's mentioned: it's not always possible /advisable to stay in that small house you bought when you were young. Neighborhoods change for the worse, far-away jobs are offered, all sorts of things happen that make moving look very attractive -- even if "upgrading" isn't the goal.
LOL! I literally said that in the next sentence of my post you quoted. (It wouldn't let me quote myself. Is that a thing?) We moved for a better school district, but into another modest home.