Why are black holes and white drarfs often called stellar corpses?

Answer 1

Once a star has become either a black hole or a white dwarf, then nothing further can happen to them. That's the end of their "life" or "history" or "progress" or whatever word you want to use.

Answer 2

Black holes and white dwarfs are often called stellar corpses because they are the remnants of dead stars. Black holes form when massive stars collapse under their own gravity, leaving behind a region of spacetime with infinite density. White dwarfs are the remains of lower-mass stars like the Sun that have exhausted their nuclear fuel and shed their outer layers, leaving behind a dense core of carbon and oxygen.