It really is odd that that attitude of the mother needing to take primary care persists even in fantasy worlds with completely differnet gender role/family set-ups, isn't it? I think a large part of the problem is that the author can say the society is equal and that women can do men's jobs- but we never see men doing women's jobs, i.e., nurturing children. If that occurred, then I think the work-children gender imbalance would be decisively corrected.
I get to play with this in Castalin. It's fun. Famous women who work hugely in the public sphere have husbands that vanish into the background and raise the kids. This is even NORMAL. (The other is also normal. Famous person = house spouse. The slightly less usual is famous important person = other famous important person. This causes people to go " . . .wow - but how do they find time? *SUSPICIOUS LOOK*")