After all, why is Yoga Day celebrated only on 21 June ?

Why Yoga Day is celebrated only on 21 June? The art of living a healthy life is called yoga. Yoga has two meanings – connect and Samadhi. Yoga contains both meanings, it is not possible to reach samadhi until we connect with ourselves. Yoga Day was celebrated all over the world for the first time on 21 June 2015, following the suggestion of Indian Prime Minister Narendra Modi to the United Nations in September 2014.…

"After all, why is Yoga Day celebrated only on 21 June ?"