They are less concerned about them having children and if they do, there is less impact to either individual because the gendered role of child care is equally

They are less concerned about them having children and if they do, there is less impact to either individual because the gendered role of child care is equally applied. Gay men take a penalty for the same reason that there isn't a default woman in the relationship who will be socially pressured to care for the child and thus increases the risk that either man will be put into the role. That isn't to say this explains all of the penalty. Homophobia leading to less employment options could also be an issue (and unequal homophobia targeted at either gender).