There are never men in advertisements for yoga only women. Sometimes there could be a few guys in a class but they always are doing perverted things or are just looking at the women's butts!! Men can not do 2 things at once so I am sure this would not be there forte.
No sport can be done by only one gender, and yoga is no exception. Many males practice yoga as well and there is no problem with it. Mens' Fitness programs at gyms also include yoga...
While many think that yoga is a sport that is only (or best suited) for women, this is not true. The same theory applies in other sports such as rugby. While rugby requires a demanding physique, and males would be better suited due to natural body build, it is not impossible for females to play.
There is simply no reason that yoga should only be for women. As others have already stated, it is great for both strength and flexibility and is not at all confined to one gender. I know many women as well as many men who both do yoga, and they both and always encouraging others.
I know many men who do yoga, one of which is my dad. It's a great way to improve flexibility and fitness and is also a good way to relax. Why would yoga only be for women? That is sexist and is stereotyping men. And since I know of men who do yoga, it is clearly not a women only practice.
The flow of Yoga can seem emasculating due to the nature of Yoga and the way society portrays the sequences. The clothing that needs to be worn can seem inappropriate for men (leggings, etc.) and it is a practice that is mainly seen being done by women in classes, etc.