Dooku's weapon was catered to his fencing style, Form II,  which was focused on dueling with other lightsaber wielders. During the generation before the Galactic Empire, Sith Lords were thought to be extinct. Jedi didn't think it practical to train to fight other Jedi since all Jedi were supposed to be good. Practical Jedi combat training at the time involved deflecting blaster beams and fighting against multiple, less skilled opponents. Thus, their weapons were suited to a different style of fighting than Dooku's.