And why does the author think that is bad?
Because it does not mention children, which is why society gets involved with marriage. If you just wanted to declare someone to be your bestie, and live together for yourselves, you would not require the recognition of the institution of marriage.
“Because it does not mention children, “
those expectations do not exclude children. They make for a more wholesome environment for raising children.
“Because it does not mention children, which is why society gets involved with marriage.”
Society got involved and the result was the marriage contract which excluded children.