Here's why:
* Main sequence is the longest stage: Stars spend the majority of their lives fusing hydrogen into helium in their core, which is the defining characteristic of the main sequence. This stage can last billions of years for stars like our Sun.
* Other stages are brief: Compared to the main sequence, other stages like red giants, white dwarfs, and supernovae are relatively short-lived.
* Stellar evolution: Stars are constantly evolving, but the main sequence represents the most stable and common stage of their life cycle.
While there are billions of stars in the Milky Way, the main sequence hosts the most numerous population.
