Simple is not easy. Teaching is neither simple nor easy. Just because a person is an expert in some area does not mean that person is also a good teacher. And just because a person is good at something does not mean that person must pursue it further. Being a teacher of yoga is not necessarily the pinnacle of yoga practice. The ability to master complex asanas does not necessarily translate into being a good teacher.

What makes a good teacher of anything? First of all, one cannot teach what one doesn't know. But it takes more than knowledge. Good teachers must also have integrity and authenticity to mentor others in the discipline. Parker Palmer wrote that
we don't just teach what we know, we also teach who we are. The yoga tradition is a powerful path to discovering the true self. Then why aren't all yogis teachers? If one is true to one's self, then the yogi is already a teacher.