If having large numbers of offspring results in high fitness, why don't all females have very large numbers of offspring?

Question

Quizplus · Accepted Answer

Females are limited by the amount of energy they can devote to reproduction in any one season. Producing and raising offspring requires significant amounts of energy and resources, so females must balance the number of offspring they produce with their ability to care for them and allocate enough resources to their own survival. In addition, some species have limited resources or unpredictable environments, which further limits the number of offspring that can be produced.

If Having Large Numbers of Offspring Results in High Fitness