Which is what mordin TRIED to do. He wanted to stabilize krogan populations back to normal levels not neuter them. Every female was capable of giving birth, it was just that the females would lose hope after giving birth to 999 stillborns and not waiting for that 1000th one. Only the krogans saw this normal birthrate as hopeless for survival (and possibly was with the females committing suicide out of despair) and went off to do their own thing.