Question

Why there are only 206 bones in humans body

Answer 1

The human skeleton is the internal framework of the body. It is composed of around 270bones at birth – this total decreases to around 206 bones by adulthood after some bones get fused together. The bone mass in the skeleton reaches maximum densityaround age 21. 

Answer 2

Because that’s all what was needed. In fact we have about 300 bones at birth which fuse later.
It’s necessary to provide a basic framework and support our organs.