Probably because, at first blush, one looks like "going forward" while the other looks like "going backward." Women ratcheting back on work to smooth life at home feels like a rejection of everything women have fought for, while men doing the same looks like an embrace of the same. That's progress, isn't it?She's overcomplicating everything.
Not as much as you'd like to think.
When a small subset of women -- those educated and wealthy enough to actually have a choice -- made the "choice" to "stay home" (I use the quotation marks because it wasn't a choice so much as a response, and they didn't really stay at home so much as redesign their relationship with work) they were a signal that something was toxic in the system. By voting with their feet they challenged a workplace structure and tempo that was predicated on the assumption that men had wives at home -- a structure that did not substantively change when women entered in large numbers.
At its core, life is pretty simple. Pick up needed skills so you can earn a living and support a family and then marry a woman who will help bring peace and harmony at home, whether she works outside the home or not. You need money and happiness, not money and more money. If you've got a good set of skills, it doesn't take too long to reach an income level where more money translates into infinitesimally small increases in happiness. It also doesn't take too long for no one at home with the kids to translate into lots of unhappiness.