Animals hibernate durring the winter because of shortage of food.
Because in the winter, there is no food for them to find, and some would not be able to stay warm. So they hibernate/ sleep through winter.
Hibernation is a process in which an animal's body temperature is lowered and its heartbeat slowed, in order to conserve energy during times of scarcity and stress.
Each type of animal hibernates in a different way. Squirrels can wake up every four days to grab a bite to eat and take a trip to the bathroom, while black bears can stay dormant, or inactive, for up to seven months with no food, water, or visits to the bathroom.