What they mean is that there is a deep rooted segregation of men and women. Especially in rural parts of India, where you can get to your mid-20s without interacting with a person from the opposite sex (not from your family i.e.). There are no social settings where you can “meet people” and hence for marriage, arranged is the only way.

“it’s tradition” isn’t much of an explanation

It’s not a moral answer, but it is an accurate answer.

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.

This book review (never got around to reading the book itself) made me understand why people think “it’s tradition” is a valid explanation at least sometimes. I disagree still but i couldn’t find any counterarguments.

https://slatestarcodex.com/2019/06/04/book-review-the-secret-of-our-success/

Not if your culture doesn’t value tradition. Yet there are cultures where tradition is ingrained in it’s value systems.