There are much fewer women competing in tournaments than men. For instance, the United States Chess Federation has less than 8,000 female members and almost 50,000 male members. So there are necessarily many fewer top women players.
Of the top notch women, some indeed can hold their own against the best male players, ie; Judit Polgar defeated former World Champion Boris Spassky in a 10 game match in 1993.
Like anything in life, motivation to excel is paramount. The Polgar sisters did not like playing in restricted women only events. They knew to improve they must play with the men and prefered playing in strong tournaments where men competed.
I am a girl myself, but I don't understand why women in general play worse than men in chess.