Perhaps because it was because the classes were reminiscent of group fitness classes that were already dominated by women. Maybe women really are more receptive to a practice that serves to catapult us past the ego and into a space of unconditionality. Women, with their gift of motherhood seem to be more able to let go of their own selfish pursuits in favor of the child. this spirit of selflessness invariably comes into play along the path of yoga.
Regardless of the reason, the practice is in no way more suitable for women and less suitable for men. After teaching yoga for over a decade it is amazing how decisive many patterns are in the behaviors of students. The men come into the class extremely tense with bodies stuck in place like the Tin Man from the Wizard of Oz. They look around them at what the others in the class are doing and they grit their teeth and try to go deeper and push harder. They are so often resistant to instruction because they are stuck in the "No Pain No Gain" mentality. Often that is the last I see of them....They probably leave feeling defeated and wake up feeling sore though they "have not done anything". Many men (and women) also look at the relaxation as a waste of time. C'mon guys, time to get real!
Yoga is a martial art that prepares one for the battle of their life...the battle with the ego. Perhaps men are more resistant to addressing and embracing this enemy. So, in lieu of men suddenly getting over themselves and embracing the grace and power of yoga, it will be up to the women to share what they are learning in bite-sized nuggets with their other half.