Why are there so few guys in yoga classes?

I go to a yoga class once a week. I have a stiffness in my neck that I find the class helps in relieving and I would also like to maintain some basic flexibility and balance in my senior years. Is there something unmasculine about this? A typical class will have about a dozen women and maybe one or two other guys. I am not overly self-conscious, but I would feel better if the mix was a little more even. It helps that the instructor is a guy, assisted by his wife.