Oh stop it, sexist mindsets LoL. Its wasn't a sexist mind set, but a money mind set. They knew all the Robin graduates could make them easy money. Thats why they got to stay. That and Damian being important to Morrison's Batman epic.
Quite frankly the Robins got hit pretty hard in their own way by this relaunch and its stupid time frame too. Not to mention how they are unnecessarily, and thoughtlessly, blending these already similar characters even further, making them less and leas distinct from one another. Honestly at this point, im not sure if it wouldn't have been better if there were less of them.