Here's why:

* Size: Supergiant stars are incredibly large, often many times the size of our Sun.

* Luminosity: They are extremely bright, emitting significantly more light than our Sun.

* Lifespan: Due to their immense size and energy output, supergiants have relatively short lifespans compared to smaller stars.

* Evolution: Supergiants are a stage in the evolution of massive stars. They form when stars with several times the mass of our Sun run out of hydrogen fuel in their core and begin fusing heavier elements.

The immense mass is what fuels their enormous size, brightness, and short lifespans.