The costs of singlehood are vastly greater than those of marriage. That has been documented repeatedly: http://www.belladepaulo.com/2014/01/getting-married-and-getting-more-money/

Maybe you are conflating marital status with parental status. They are different. Some single people have kids and some married ones don’t.

That part about marriage being the “only game in town” for raising children has been debunked repeatedly, too: https://belladepaulo.medium.com/are-single-mothers-messing-up-men-scientifically-based-grounds-for-skepticism-24e5537e11fc?sk=de079a0cce8854ef84edc4a0376fc115