The automobile spreads people out. Historically both spouses would have worked on the family farm or helped run the family business, which is close to home. Industrialization led to the suburb as factory workers tried to move away from polluted industrial sectors. Because of the car work distinct from the household became feasible.
Discussion
For a while, the West was so rich one parent could work and earn enough to support the family. At the same time, single-family households became the norm, so now one parent needs to stay home to care for the children.
The middle class isn't so wealthy any more, so now both parents have to work. But grandparents don't live at home, so parents have to outsource childcare so they can both commute to their jobs. But now you're effectively paying someone else to do the full-time job of caring for your kids, and that second income stream is all but a total wash.
The solution is tight-knit communities where multiple families or multiple generations of the same family can share the responsibilities of childcare.
The work-from-home trend is positive, as well, since it brings the household business back close to home. Interestingly, that's only made possible by a shift to a post-industrial economy.