Why might a group that lobbies for an end to gender discrimination see more free rider members?

I believe the answer is: Because So many people benefit from it that most members have little incentive to take an active role themselves.

Compared to the past, female citizens now have much more freedom and opportunities. So, most female that was born while experiencing the fruit of effort from past activists do not understand the struggles that the females have to face during the early age of activism

You could solve them by trying something new that everyone can agree on or make a decision too.