Boy, it sure is convenient that all these girls just want to get knocked up
Mostly likely because there is lack of men around, because of war and life threatening jobs, reducing population of men.
So, rather than just trying to find a good life partner in such troubling times, it's easier to just get knocked by some random dude and raise the child alone instead.
And the best place to get dudes to knock up while as bonus earning some money, is a brothel. Because it's all no strings attached.
Plus, the girl can even select on whose kid they would like to raise, depending on their prefered types (since physical features are somewhat hereditary).
I mean, these are prostitutes who are basically barren for life thanks to the harsh medicines they've imbibed. Not that surprising that a number of them do actually want kids, when able to choose so for themselves.
Well not every girl is barren though.
Some weren't lucky enough to get knocked up, and some didn't yet find a preferable man to get knocked up with (I mean, those prostitutes do get variety of customers but not everyone would be upto their prefered type, whose kid they would like to bear).