Surely this one of the main reasons...

http://news.bbc.co.uk/2/hi/south_asia/6320413.stm
Casteism is fundamentally no different from racism. However, where racism is abhorred all over the world in an educated society, casteism is still practised in a large section Indian educated class.
Find the following:

``Like many Indians, Sowmya's parents wanted her married to a groom of their choice - one drawn from the same community of high-caste southern Indian Brahmins.''

in the following link.

http://news.bbc.co.uk/2/hi/south_asia/6279287.stm