Answer by Arpita Yadav:
Because of them!
4 log dekhenge to kya kehenge!
( Rough translation: What will the society say? )
In India, the parents are very much influenced by how the society perceives them or their children. Many a times, the reason cited for decisions is that it does not look good to the society, or that they(the parents) do not want their neighbors or far-off relatives to be talking ill of their daughters. It is a matter of social dignity for them. And because if a girl does not marry at a "decent" age, the society starts talking of there being some fault with the girl, and that this becomes the opinion of everyone around. To save themselves from this situation, Indian parents try marrying off their girls at the so-called "decent" age.