Living in SF, the very real phenomenon I've noticed is friends who hit late 20s/early 30s, get married, and then leave with varying intentions but many to move

Living in SF, the very real phenomenon I've noticed is friends who hit late 20s/early 30s, get married, and then leave with varying intentions but many to move closer to their parents (presumably in a cheaper area) so that they can get help raising kids while both continue to work. This article doesn't really capture the fact that this only works if the 30-somethings move out of SF, NY, LA, etc. to move closer to home (unless those are the places where the parents are already living), which may be an area outside of a major urban job center.