There are all kinds of societal benefits to a committed family unit. The difference in criminality, educational attainment, wealth acquisition, etc, among child

There are all kinds of societal benefits to a committed family unit. The difference in criminality, educational attainment, wealth acquisition, etc, among children raised by single parents vs coupled parents is staggering. Of course you can be a committed couple without the need for marriage, you can be married and in no way committed, and you can be married without kids, so it's not a perfect incentive structure...but I think that financially incentivizing a structure that removes burdens from the rest of society is definitely a good idea.