The start of Yogic tradition cannot be dated because the ancient Vedic traditions were passed down from teacher to student in the oral tradition. I was not until around 250 AD that the Yoga Sutras were written by the author, or authors Pentanjali. Gurus could be either men or women, but men made up the bulk of teachers. I could go further into the social structure of Vedic culture, but I won't for brevities sake.
Flash forward to the 20th century. Gurus from India came to America to spread the word of Yoga. You had Paramhansa Yogananda, Maharishi Mahesh Yogi and Swami Vivekananda to name a few. When Yoga was embraced by the counter culture movement, it was stripped of it's traditional aspects like spiritual discipline and shunning of intoxicants. What was the original eight limbs of yoga, became one mainstream branch of Yoga, called Hatha Yoga. Now, when I mention Yoga to people, they think of it as a bunch of stretches and poses. I don't know how this happened, but somewhere between 1970 and now, Yoga became entwined with feminism. Maybe it's just the ideological alignment with the counter culture and it's roots back to liberalism.
So what is a dude to do? If you want to build body mass, Hatha Yoga is not the way to go. From the outside looking in, a Yoga class looks nothing more like a ballet class. This is why I try to focus on the Yoga Sutras. Hatha Yoga is introduced around 1500 AD as a method to prepare the body for long bouts of meditation. It's not a means to an end in itself.
If you are a man, consider this: Yoga works to help us overcome emotionality based decision making, and replace it with rationality. How often do we see people making decisions based off emotionality? We are so conditioned to be in tuned with our feelings, that we mistake them for a reliable compass for decision making. Are you following your true instinct, or your emotional instinct? If you do not do the work to become self aware, you will never know.
If there are other reasons why, please comment below. I would like to know so that I can make traditional Yoga more palatable to men.