Marriage is traditionally a terrible bargain for women, but it was the only choice they were allowed to make. Now, they can make their money and buy property and have kids on their own.
A lot of men haven't realized the era of the provider is over and dead, and they're now optional. They have to make women want to be with them, and a lot of women just aren't willing to compromise on equality these days.
In most western countries, low income women do not become much poorer if they become single mothers. In some places, it increases their living standards. But for upper middle class families, a breakup tends to be costly.
Also, there seems to be shared causal factors that lead to both stable relationships and financial stability. Such as impulse control, mental/physical health and the ability to postpone gratification.
Cool, child support and alimony optional now. Right? Because it's always easy to be independent with OPM. People forget single moms became far more practiced after the state incentivized breaking up families.