Ok, new marriage procedure:
people who ARE married but want a divorce are really NOT married because they have decided together that their marriage is invalid.
People who are NOT married and have no intention to marry, but are cohabiting, really ARE married because of fidelity.
Yup. You have it right.
Apparently, many cohabitating couples do so for financial reasons. “Married, filing jointly” does not appeal to all. But mostly it’s probably men who can’t commit, again for financial reasons.