Here's why:

* Supergiants are stars that are significantly larger and more luminous than main-sequence stars of the same spectral type. They are characterized by their enormous size and incredible brightness.

* Red supergiants, in particular, are the absolute largest stars known. They can be hundreds of times larger than our Sun.

* Blue supergiants, while not as large as red supergiants, are still significantly larger than our Sun.

It's important to note that the terms "large" and "massive" are not interchangeable when discussing stars. While supergiants are the largest in terms of physical size, the most massive stars are often found among the blue supergiants and hypergiants.