Simple.
Once JNU was given to Leftists by Indira Gandhi, they controlled recruitment process. Thus only leftists got jobs in JNU.
There is a running gig in Delhi that if you want job in JNU, at lest refer to Marx a couple of time (do it properly as these professors know Marx inside out) and blame corporates for poverty in India, when you go for interview of Lecturer post.
It is a process of self selection, and this has been done in Nalanda university also. I have read somewhere that a staff member accused Amratya sen and then registrar of Nalanda university stocked that university with JNU leftists.Though in this case all is not lost as because of immaturity of their tenure, they could not influence recruitment much and GoI could still fill vacancies with right wingers.
@magudi
@ranjeet What happened? Did it involved a girl.