Explanation From Original OP:

In India like in most cultures it was considered preferable to have a son, however in India, having a daughter meant a heavy financial burden for the family since it is a custom to give a dowry (goods or lump sum of money) to the husband of the daughter when she got married

This lead to many poor families to simply kill their infant daughters if they had any since the family did not want to commit to a hefty dowry.

Ultrasound Technology became first available in the 1980s in India and then became widespread in the 1990s which slightly curbed the infanticide problem. However, ultrasound technology now caused a massive increase in Feticide (removal of fetus) since now parents could use ultrasounds to find out if their unborn child was male or female, and if it was the latter, the fetus would be removed

This prompted the Indian government to ban the usage of ultrasound technologies for the purpose of finding out the sex of the fetus in 1996 because their demographic shifted massively with there being more men then women

Sources

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Source 2

Jesus Christ, India…

That is by far the dumbest matrimonial tradition I’ve ever heard about. Not only do you give away your daughter to the other family, you also have to bribe them to take her?

Who the fuck figured this will work.

It’s fairly common across cultures, due to the highly transactional nature of pre-modern family formation, for families to pay either dowry or bride-price. The former usually when labor is plentiful in society ("I have enough people already; you want me to take another mouth to feed? Pay me"); the latter when labor is at a premium ("My son needs a work-partner-I mean, wife! I’ll give you a good price to give up a pair of hands from your own farm-I mean, family!")

That makes sense but then why do these things remain even when the labour supply/demand changes

Traditions take generations to change, and change this past century has been… very rapid.