Here's why:
* They are arboreal: Spider monkeys live in trees, and spend most of their time in the canopy.
* No nest building: Unlike some other primates, they don't build nests to sleep in.
* Sleeping locations: They typically sleep in tree forks or branches, using their prehensile tails for support and balance.
So, while they might use a branch as a makeshift sleeping platform, they don't construct traditional nests like some other monkey species.