There are many answers to this question. We can even count lots of reasons for that. The most simple one is that through Yoga we can get HAPPINESS. Everyone seeks happiness, but people usually look for it outside themselves.
Yoga helps us understand that HAPPINESS must be sought inside ourselves because HAPPINESS actually means harmony of the body, mind and soul. By practising Yoga postures, breathing exercises and meditation, one can reach that physical, psychological, mental and spiritual equilibrium that is the source of happiness. If correctly and perseveringtly practiced Yoga can offer a state of health and body harmony. It actually offers countless ways to improve our life and destiny, to enlarge our personality and attain self-knowledge.
Yoga can increase our state of awareness and urge us to a spiritual experience toward our being. The sublime aspects that Yoga can enforce inside of us will bring some unique touch that helps us discover the divine sense of our life integrated in the Absolute.