Why pokéballs?

[Setorines]

Well odds are the pokeball was created before the Pokemon. If evolution teaches us anything it's that humans would never survive in an environment where the animals can breath fire, or shoot water, etc. meaning Pokemon were a science experiment.

To add to this when surge is meet there is a mention of a great Pokemon war recently which goes to show that these creatures of science were created with the intensions of war as are most great inventions.

Now with this said it seems logical that the way to control these creatures would also have a method of release that allows for a moderate distance and quick reaction times. ie. a sphere.