Here's why:

* Main Sequence Stars are Most Common: The most common type of star in the universe are main sequence stars, like our Sun. These stars are fusing hydrogen into helium in their cores.

* Red Giants are a Later Stage: Red giants are evolved stars. They are the result of main sequence stars exhausting the hydrogen fuel in their core and expanding.

* Limited Lifespan: The red giant phase is a relatively short stage in a star's life compared to its main sequence phase.

Therefore, while red giants are important in stellar evolution, their limited lifespan means they are not the most common type of star.