Kapłańska 23:6 Odniesienia do Talmudu: Sukkah & Kiddushin

R. Yohanan answered in the name of R. Shimon b. Yehozadak: It was stated with regard to Sukkot, "The fifteenth," and it was stated with regard to the Festival of Matzot, "The fifteenth." Just as there the first night only is obligatory but from then on it is optional, so too here the first night is obligatory, but from then on it is optional. And from where do we know [that the first night of Pesah it is obligatory to eat matzah]?

Rava said: It is necessary, since I might have said, derive [the law from a similar case] of the fifteenth, from the fifteenth of the Festival of Matzot: just as there women are obligated, so too here women are bound. Therefore he taught that [women are exempt].

If so, Matza and Hakel are necessary to teach me that women are Chayiv. So why do we need both?