Natural selection selects for what works well enough. In a more rapidly changing environment, adaptability is what often gets selected for. But in the case of species like the kakapo that live in stable, slowly changing environments, it selects for reproductive stability. The kakapo has a fairly intricate, complicated reproductive cycle that requires specific conditions. This effectively results in their population growth being very very flat. Good for environments that are incredibly stable so they dont really experience boom and bust cycles but if they find themselves in a rapidly changing environment, their population crashes and they dont recover quickly.