I wonder why in single player mode Pokemon trainers (some of them even exclusively) use Magikarp that only knows how to perform Splash. According to this question Splash never even does real damage, unless it's out of PP which takes way too many turns to be a feasible tactic, but who knows maybe that is actually what they're going for? I kind of get that fishermen could employ this tactic, as they probably have a lot of patience fishing their whole life, but why would the real trainers try to… Are they leeching off their opponent's PP this way?
Is there any explanation why a trainer in single player mode would fight somebody with Magikarps that don't know any other moves than Splash?