It's been more than a generation since women started making more money than men in some households due to increases in equality between the sexes. The phrasing and positioning used implies that a stay-at-home dad is something that we should be reacting to as an economic problem.
In other words, it required the assumption that men are the proper breadwinners in heterosexual households.
Members of households all need to contribute, and while I am neither female nor married, I have heard from many married females that unemployed men do not generally tend to assume the duties of housekeeping. That is to say, the wife winds up both breadwinning and housekeeping, and the man does not contribute. This is broken.
It's sexist of me to generalize (and certainly I hope if I wind up married and unemployed, I won't let my partner take all the burden), and it may well not be what the author was thinking of, but if we take feminine anecdotes at face value there are more reasons to encourage men to be breadwinners than simply because it's their role.
And salaries for women still tend to be lower than those for men. Is it sexist to point this out?