LU -“In the case of marriage, according to halacha, a girl can decide that while it is a Mitzvah to get married and have children, it would not make sense for her to marry someone whom she does not want to marry (for whatever reason) in order to fulfill this particular Mitzvah. While a boy should also not marry someone whom he really does not want to marry,it seems to me that his reasons would have to be more substantial than a girl’s would since he does have an obligation to get married.”
They both have a Chiyov, but for different reasons! If Rav Leff said it’s just a Mitzvah, he made a mistake!