That statistic sounds totally wrong and after looking at your source it is highly misleading. It’s just if the parents were married at birth.

Of the people I know with kids like 50% of them were not married when they started having kids. They either got married latter or never married because there was no advantage to do so and they didn’t care.

Yet none of them are what you would call “single mothers”. They are all still together with the fathers of their children.

So basically it says more about marriage than it does about parenting.

If you have better data I'm happy to look at that. I agree that cohabiting are likely more common now and it is possibly more common to get married just after birth than it used to be.

Table CH-1 from this census website shows that children living with a single parent goes from 10% in 1960 to 36% in 2020. (=E13/C13) I'm not certain but I think they are accounting for cohabiting parents here because they don't use any language related to marriage and the census could tell if the parents were cohabiting or not.

https://www.census.gov/data/tables/time-series/demo/families...

>>>No change, I expect, in the children's suffering

Drug use, gang activity, and other criminality are all positively correlated with single-parent households, and some data shows even MORE positively correlated with single-mother, as opposed to single-father, households.

https://www.ojp.gov/ncjrs/virtual-library/abstracts/single-p...

https://www.researchgate.net/publication/316649639_The_effec...

https://www.heritage.org/crime-and-justice/report/the-real-r....

Again, we can go deeper. How many single mothers would be forced to remain in otherwise abusive situations but for the fact that she is able to both work and care for her family due to “progress”?

My cursory look for some evidence suggests single mothers see dramatically elevated rates of violence and abuse. This source surveys children who live with both parents and just one. Children living with just one are seven times as likely to have witnessed someone hitting their mother in the past year than children living with both parents. I take that to mean that the increase in single motherhood means there is more domestic abuse happening than if no such increase had taken place.

https://ifstudies.org/blog/children-in-single-parent-familie...

Or maybe those women are now single mothers because they were able to escape their abusers. You would have to compare data across decades, and adjust for people being more/less willing to disclose abuse.