>>37963755>power of friendshipThe biggest and most powerful option because of the nature of the Pokemon universe. The trainer and their team are all steadfast friends who will stick with each other through thick and thin, whatever their adventure throws their way.
>sense of obligationThe phrase "they raised me, after all." Has a lot of power too it in a number of human societies, it's possible Pokemon reflects that.
>pokeball brainwashingThe stolen Purrloin subplot in B2W2 could be the horrifying undercurrent of the Pokemon world.
>drive and ambitionMaybe they simply recognize that the human is going for the top and want to be a part of that. Maybe Pokemon don't naturally have the push to grow and succeed, and they need a human to push them towards fulfillment.
>access to human resourcesIt's possible the Pokemon is siding with the human so they can rest at Pokemon Centers, or take advantage of huge Pokemart stocks, or what have you.
>mutual goalsCould be that the Pokemon's wants in life simply align with the trainer's, be they adventure, success, or whatever else, making this a mutually beneficial partnership.
>trainer's training and strategyPeople hire personal trainers all the time, and only a prideful lunatic is going to turn down sound strategic advice. As much as the trainer is taking advantage of the Pokemon's power, maybe the Pokemon is taking advantage of the trainer's strengths too.
>pokeball quickdrawMaybe the threat of instant solitary confinement is enough to get them to cooperate.
