Because the laws of the Pokemon universe are a Pokemon Apartheid, where only humans can vote, and even hyper-intelligent Pokemon with 4000 IQs are forced to sit in little balls in boxes if they don't act exactly as their master race dictates to them...
Because humans can learn more then 4 moves at once. And if all else fails, multiple trainers could all gang up on one pokemon to take it down. And yeah, what he said.
