Is it that marriage itself is beneficial or that people capable of maintaining a relationship make better parents? Divorce is significantly more common for bipolar, paranoid, and schizophrenic people for example. So I think we need to look at widows or something to control for those kinds of issues.
In my personal opinion. I think what she’s stumbled on is yet again proof of Americans hyper individuality rearing its ugly face. The Europeans can stay together longer without the marriage piece of paper because
1) Selfishness derived from hyper individuality doesn’t drive people to nope out of relationships at the first sign of minuscule problems or one side not getting their way
2) Since over there not everything is an economical benefit proposal people value the relationship with different metrics than our countrymen and women do.