Its probably cause Women think its risky to hold or invest in crypto-currency not everyone but yes majority of them according to my personal experience, even though Women are better with handling money imo.
The amount of women at bitcoin events is only as high as 21% because 1.) they do better in social situations and 2.) Im guessing some of the women who get hired to promote at events at increasing the averages. Honestly not sure women are better than men with handling money, how do you figure this ? hehe