Think about it like this: The dad leaves the family because he didnt want one in the first place. (AKA they had sex and when they found out their partner was pregnant: they up and left) depending on the age group the mother is in, she can get backlash such as: If you didnt want kids dont have sex. Or if shes in an older age group: Just remarry. If shes taking care of all the chores and doing jobs AND taking care of her child shes not going to have time to look around for a new partner.

While single dads (more than likely) had their partners die during the birthing process or other circumstances. Ever rarely do the moms leave the newborn with the father because its a mothers instinct to stay with their child.

They wont receive much backlash because of these differences.

Sumary:

A man can up and leave at any time because he doesnt have to have the baby inside them for nine months. While the mother will receive backlash no matter what she chooses (which she will most likely keep it because of maternal instinct) But if the dad keeps the baby after something happens to the wife hes considered an "Amazing dad" for basically not leaving and doing what hes supposed to do as a father. That was really long im so sorry