It’s just another way for getting money
Imagine you create chocolates which are decent good To sell initially you should sell chocolates for decent price when your Chocolates become famous you will increase the price hence you will get more money
Same happens in the case of Srm even if a department has some 900 seats they sell the initial 600 seats for normal fees under the name of Category-A and when the people are keen they will increase the price of same seats to double the normal seat price and sell the seats with name Category-B making people fools around.