Good for one is not a good marriage. Nor is a partnership. It's indentured servitude.

Nobody leaves a good marriage. Divorce rates started skyrocketing before the advent of social media, so nice try but no dice there. Your attempt at an explanation also doesn't account for all the grey divorces. Plenty of women out up with a lot of shit for this of the kids and ride it out to file for divorce as soon as the last one has fledged.

Because it wasn't a good marriage. It was an isolating, sexually frustrating, lackluster, lonely one.