>>49418923They don't shrink voluntarily, who said that? The drugged up primeape got so weak it just went into the glasses case on instinct. Similarly pokeballs take advantage of this instinct and involuntarily makes them activate this power and get in the ball. They try to break out because it was involuntary containment, that's pretty obvious.
Think about it, they're called Pocket Monsters in universe so you'd have to assume they'd be named after the fact that they all possess the ability to fit into small containers.
