> I took the parent comment to mean that being married itself shouldn't provide any more benefits than just being in a stable, long-term relationship.

Understood. I still think it's fair for the burden of proof to fall on the people trying to explain away current demographic trends. Just because possible mechanisms don't line up with expectations doesn't mean the outcomes aren't actually happening.

And, at some point, there is a distinction without a difference when talking about long-term monogamous cohabitations that do or do not involve a wedding ceremony. In common law, it would be a marriage either way. Maybe the real question is why common law marriages aren't recognized more often now.