I read it as people taking that step in a relationship without much thought because that's what society has conditioned us to believe is normal and then divorcing like breaking-up.
Marriage brings specific legal and financial benefits, depending on the country (married couples tax allowances, spousal rights to pensions and inheritance etc, spousal privilege in court, visa/residency rights, child custody rights).
As these benefits have reduced over a few decades, the number of marriages has gone down (at least in the West?). I don't think that's a coincidence.
You don't need a legal marriage to share a loving and fulfilling life together with a partner. But, if you do share a loving and fulfilling life together, marriage might benefit you for one or more of the above reasons.
If people thought of marriage as nothing but a legal contract, likely to be broken, and acted rationally then I expect they wouldn’t bother at all: the benefits aren’t particularly great while the risks are large.
I think we probably mostly agree with our own opinions but perhaps disagree on the opinions of others.