Yoga: Why people who practice yoga do not give importance to Yama & Niyama the first 2 aspect of Astanga Yoga?

Some people are interested only in sweets and not sour. Some take sour so that they can take more sweets. Yoga also is taken like a gymnastic performance and not as a part of 'sanyas'. But, a sanyasin should practice yama and niyama as most important than anything. Yama and Niyama are not a part of a 'Yoga' but part of the life-style for day-to-day life as per the advice of our forefathers.