Because they enjoy the exercise. Ha ha.
Who knows, that might be true, but scientists have discovered that bees dance to communicate. Different dances, coupled with sounds, can tell nest mates the distance, direction, quality, and quantity of a food supply.
The “round dance” says the nectar is less than 32 metres away. The “scout” bee turns in circles to the left and the right. The richer the food source the longer and more vigorous the dance.
The “waggle dance” tells other bees that the food is more than 32 metres away. The scout makes two loops with a straight run in the middle. The direction of the straight run shows where the food is.