They could choose to live closer to work in many cases
And what about when different people in the household work in different places?
Up North it is very, very normal for one half of a couple to work in one city and their partner to work elsewhere.
For example, DH spent a while working in Sheffield, and then Leeds, while I was in Manchester.
I spent a while working in Liverpool, then Leeds, then Manchester....we couldn't have moved every time.
Where I live now, I have close friends who work in Leeds, Manchester, Sheffield, Liverpool, Bradford, Nottingham, even Leicester. It's not as easy as "moving closer to work" when you and your partner are in the sort of jobs that could see you working all over the place.
Sometimes it seems like many MNetters think people "up north" don't have the sort of professional jobs with long commutes that people do in London. If you don't believe me, look at the m62 travel updates in a morning, or the m1 between Leeds and Sheffield. These aren't people out for a fun morning drive.