Why do squirrels spin on bird feeders?

There is a type of bird feeder in the market with the name of Droll Yankees. This bird feeder has the advantage of spinning with the weight of a squirrel. When a squirrel tries to get the feed from it, due to the squirrel’s weight, the feeder will start to spin, which results in a loose grip of the squirrel over the feeder, thus protecting the bird feeder from squirrels.