The comparison between the nuns and th knights is not valid.  The nuns were all members of religious orders.  The knights are not a religious order, but something else altogether, although exactly what they are may depend on what they need to be given a particular circumstance.  Finally, obviously, the nuns were women, and thus in greater need of oversight by the men who run the church.  As we learn in Genesis, women are prone to the wiles of the serpent and have to be kept under scrutiny.