This really tells you how "bad masculinity" pervaded everything. I'm speaking of the designers here, not the astronauts. Why not a diaper also for male astronauts from the beginning? Isn't manly enough? Does it show weakness, like a toddler or an old dying man?
I think the designers just didn't think of it.
Women also started with a feminized version of the uncomfortable device and then switched to diapers, and then men followed.
It's possible there were no women on the design team but I don't think it's a case of bad masculinity.