The guys know it. When you decline the invite, as I did recently, it's assumed you're on overload. Actually, none of the above reasons applied when I declined. My talents, skills and time would be better suited elsewhere. It is my contention that women who have served on nonprofit boards do become overwhelmed with the amount of time and energy they are expected to volunteer.
Some nonprofits use their board members as free employees.
For women seeking to serve on corporate, for-profit boards, nonprofits are a good beginning. They do give women the chance to showcase their skills and talents. On the for-profit side of serving, men spoke out. Not surprisingly, they wanted confidentiality. I am convinced they hit the target when they expressed their fear.