Initially caste based quota was chosen because they were discriminated against by the society for a really long time. The profession one would go in was based on the caste they were born into. A barber's son would be barber, a cleaner's son would be cleaner. Here is one example : http://en.wikipedia.org/wiki/Devadasi . People from certain caste are still socially backward while other caste have managed to come out. The problem is the reservation system is not reformed based on that. This is a topic of hot contention.