Why do the stars in a stationary state belong to the main sequence?

More than 90% of all stars are in a stationary state and are located in a certain band on the Hertzsprung-Russell diagram, therefore this band was called the main sequence.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.