Why is the data connection non-persistent in FTP? What advantage does this offer over keeping it as a persistent connection?

The control connection in FTP is persistent but the data connection is created and disposed after each data transfer (aka. non-persistent). What are the advantages to making the data connection non-persistent? Does making the data connection non-persistent free up resources for the server?

So that end of file equals end of stream, so that there doesn't have to be a superimposed protocol on the data connection.