I honestly didn't think about it until now. There's several practical concerns with menstruation, and forced birth control is an actual part of human trafficking because people want the people they buy to work as much as they can.
In a darkly realistic scenario, sterilization could be a cold economic decision. Or a psychological thing, where it's just another way that the zako isn't allowed to imagine themselves as anything else.
But you can come up with a million ways something can be shitty, and the idea that the zako no longer have the ability to have kids even if they wanted to is just... sad, man.