maybe its associated with it's ability to cause rain?How in blazes is Pelipper able to use Shock Wave?
you know how lighting is created in nature?
You know why during rainstorm we have storm clouds and lightings?
The wet air that is high above is cooled down the higher and near the cosmos.
Ice particles that are high up in the sky rub and create (-) energy that seeks the fastest way to get neutralized and conducts with the ground(+).
Practically ice types should be able to learn this.
Maybe Peliper if can summon rain, use ice attacks also should be able to produce lighting even if itself is weak to it when hit by it.
Remember even humans can create energy but that what hurts is the hitting by near/close contact. Like when you are electrized and touch your car then the energy you feel realeased as fast "heat". The energy only hurts when maintained to long or to long exposure thats why it's own attack would not hurt it, bc it's directly created and realesed energy and not hit by without preparation. Interesting would be if they would use Show Wave Pelipper as a defense mechanism against Pikachus attacks.