Well, for one, they're called under and never used for a reason. You won't be seeing them just anyway.
And besides, it doesn't take much knowledge to know to use super power rather then ice punch on an Azumarill or whatever, so actually, it doesn't take much knowledge to know how to use ditto. It just requires that you are familiar with moves and types.
aka familiar with most of the metagame, which is what I said