That's because people were more circumspect about who they married.
And also because there was not this pervasive sense of entitlement that makes people impossible to live with.
I have heard this fact for a while as well. I also figured it had something to do with people’s morality. What I mean by that is that people who think it is morally right to wait to live together until after you get married probably are more likely to have a moral worldview that is against divorce. Does that make sense since I know I can be wordy at times?