Indeed, if you stare at the bar chart for a moment, you'll realize that a sufficient explanation is that women more often have the option to reduce their hours or stop working entirely. In our culture, men generally don't have the privilege of doing so.

I've lived this myself and also watched many instances of it in friends and colleagues. Is anyone really shocked by the idea that new mothers might decide they'd like to stay home and raise their kids?

As a man, I'd almost have killed to stay home and have my wife keep working, but that's just not how it is.