In theory both the mother and father have equal ability to just walk away from an infant (or a 10 year old for that matter).
In reality, the number of fathers who are behind or just not paying child support are pretty high. The number of non custodial mothers paying child support and behind on it is pretty low.

This is the area that's not factored into your analysis. The commitment for a woman isn't just the 9 months. Very few infants are given up for adoption in the U.S.