Many people competing for the same jobs drives wages down. More than half of households are dual-income households.† This increases the labor pool, which drives down prices.
Ironically, it would seem that, if more families switched to one parent being the primary breadwinner, it would drive up the cost of labor and make single-income households a more sustainable proposition for more families.
The knock-on benefits from the additional time and attention the now stay-at-home or part-time working parents could give their children would have a generationally positive impact on well-being and prosperity.
† Bureau of Labor and Statistics: https://www.bls.gov/opub/mlr/2020/article/comparing-characteristics-and-selected-expenditures-of-dual-and-single-income-households-with-children.htm
Wild take: reducing the individual work hours to 20 a week would also make labor more scarce and thus force wages up up.
Sure, having many people work relatively few hours per person is significantly less efficient than fewer people working long hours but as with everything, there's also a tradeoff: efficiency vs xyz.
Not every job can be done in 20 hours per week. Some can, though, and in such cases we should pay people for output rather than for time. That would make certain career fields more conducive to family life, because a hard-working breadwinner could do all his work in under 40 hours, and have more time left to spend with his family.
