Оставшись без своего единственного естественного врага, рыцари размножились чрезвычайно
The last dragon tried to talk his way out of it. Was mumbling something about consequences and the last breath curse. But nobody listened. King said "Off with his heads" and in three axe swings the dragons were no more. Three castle gates were furnished with heads (fourth only got tail, but nobody used the gate anyway). And everything was great.
Then, left without a natural enemy, knights population grew...