Someone has to record it.
Someone has to distribute it.

Producing a song requires a lot of talented people and a lot of expensive gear. The record label is an organization that brings all the elements together to turn the song into a marketable product. They put the money up, sign artists to recording contracts, get the songs from the publishers, schedule the sessions, oversee the production, and distribute the final product to both national and global retail markets. The royalties on the record are separate from those on the composition so like the publisher, the label must become a channel that receives royalties from numerous sources and distributes a percentage of the royalties to the artist and often the producer.