Some people practice yoga to get stronger. Some do it to get more flexible. Some do it to relax. Some do it for the community. Some do it to lose weight. Some want a nice butt. None of those are bad, and I don't think there's a wrong reason to do yoga. Yoga can benefit everyone in some way or another.
I practice for the mental aspect. The way it makes me think, or not think, or think about thinking. The way I can learn to see my thoughts without judging them. The ability to be compassionate with myself and realize that everything is temporary and I'm exactly where I'm supposed to be.
Why do you practice?