* Their anatomy is optimized for climbing and swinging: Monkeys have strong limbs, grasping hands and feet, and flexible spines, all perfectly designed for moving through trees. Wings would hinder these abilities.
* Flight requires significant energy expenditure: Flying is energetically expensive. Monkeys have already evolved to efficiently move through their environment using their limbs.
* Their diet and lifestyle don't require flight: Most monkeys eat fruit, leaves, and insects, which are readily available in their arboreal habitat. They don't need to fly to hunt or gather food.
* Their evolutionary history: Monkeys are primates, and their ancestors were primarily tree-dwelling creatures. They never developed the necessary adaptations for flight.
Evolutionary history: The lineage that led to monkeys and apes diverged from the lineage that led to birds millions of years ago. Birds developed wings and feathers through natural selection, as these features were beneficial for their environment and lifestyle. Monkeys, on the other hand, developed the adaptations that made them successful in their arboreal habitats.
In short, monkeys are highly specialized for their existing way of life, and wings would be an unnecessary and potentially detrimental adaptation.