Endogamy is one of the practices that took root in Indian society as a way to enforce the caste system. Some scholars even call it the rationale behind the caste system. It's got it's roots in Hindu scriptures (not hating on the religion, but it does need reformation IMO).
To read more about one of the foremost Indian/subaltern scholars on this explanation (endogamy) - https://baws.in/books/baws/EN/Volume_01/pdf/20
P.S I think proximity to India, trade with India could have lead to the practice being observed in Afghanistan, but it also seems like Islamic clergy (majority practice this in Afghanistan) does not have entirely progressive views on this.
Idk it always seemed like knowing that gender is a social construct / or performance clarifies how to resolve the exploitation of people in the working class who have to perform oppressive roles because of their gender. It really is emancipatory as in it allows no linkage of production roles with biological attributes, for starters. And even allows the working class to stop dividing itself on the basis of gender. There will always be short sighted or selfish actors who turn the movement towards bourgeois interpretations.