Here's why:

* Density: Black holes are incredibly dense. Imagine squeezing the entire mass of our Sun into a sphere smaller than a city. That's the kind of density we're talking about! This density arises from the collapse of a massive star at the end of its life.

* Gravity: Due to their extreme density, black holes have immense gravitational pull. This pull is so strong that even light, which is the fastest thing in the universe, cannot escape its grasp.

That's why we call them "black holes" – they are regions of spacetime where gravity is so intense that nothing, not even light, can escape.