I agree with all of this and had similar marital benefits. It’s still a risky proposition. I dated for 7 years before proposing and we had lived together for a few years and I was in my thirties by then. Not saying this is the best recipe. But I think it’s just not something that should be rushed. When I hear about people meeting and being engaged a year later I just can’t fathom that working (I know it can and does, but I think it introduces a ton of risk).
I suspect it has little to do with education. It’s more about not doing the “traditional“ marrying a high school crush to get laid/because you got knocked up, taking time to learn who you are, and dating around to find the right partner.
The thing I don’t think these statistics always reflect is the societal changes over the decades. Why people marry, when they marry, ease of divorce, the effects of widespread divorce on upcoming generations, it’s all changed enormously over time.