This is something Americans say, but we have empirical data that it’s not true. Compare poor Asian Americans, who have very low divorce rates (similar to rich Asians), to poor whites, who have very high divorce rates. Poor Asian kids have double or triple the chance of becoming upper middle class as adults compared to poor whites. Mormons, another group that emphasizes family stability, also have much higher economic mobility than other whites. As Charlie Munger used to say: figure out what works and then do it.
My parents are Asians who don’t get along, while my wife’s parents are white people who have been divorced three times each. Her parents are happier, but my life was easier and opportunities came much more readily. Divorce is a great way to turn a solidly middle class family into two financially struggling families, disrupt kids’ education, extra-curricular activities, social circles, etc. And it doesn’t end when the kids grow up, because that strain of financial resources continues into adulthood when parents come to depend on children.
Americans are rich enough where imposing those costs on their kids isn’t fatal. But imagine you’re in a third world village, and at the edge of survival to begin with. Your mom and dad are “no longer in love.” Dad leaves, and the mom and kids starve to death immediately. That’s why most traditional societies have strong norms against divorce.