Bees need honey to survive the winter, but they make way more honey than they'll ever eat. That left over honey sits in the hive and crystalizes, and the bees can't use it after one season. It takes up space and that makes the bees swarm, which could drive them to move into someone's house/property where the house owner may try to kill the swarm. Old honey is hard for bees to eat. Bees make as much honey as they can, they don't ration it, and they don't stop ever. Because of human activity bees are in trouble and honey bees need people to help them stay disease free and protected. Most people can't afford to keep bees without selling the honey and if you didn't harvest it would end up being very messy and hard on the bees.