It's based on the light novel not the web novel. You should have seen that when Glass appeared because she too wasn't in the web novel.
Also it's not an infection but a breeding parasite.
The problem can be broken down by society standards and the phenomenon of the marriage market.
Basically the most important attribute for a female is and always was her capacity for child bearing. For a men however this is only important for his offspring because offspring of others are a...