Because several million dogs named Fido or Spot would get mighty confusing?
97% of my dogs have/had “human” names.
The others had an Irish myth, “Pooka”, one has a Norse god, Odin and the other has a number, Seven.
Most of my snakes have “human” names, too.
What else would I name them after?
States?
Minerals?
Cereals?
As opposed to several million humans named Jerry?
I've had seven (human) kids, and let me tell you - figuring out names for them was tough. Animals, not so much. You can call 'em whatever strikes your fancy.
Some of my dogs' names over the last 50 years:
Zero
Stogie
Timber
Terra
Sugar
Princess
Baby
Buda
Peanut
Rusty
Zeus
I can make up dog names all day long without ever running out of ideas.