What I'm curious about, though, is that how do ten people write a track together? And then six people produce it. What do all those people do? I'll answer the latter part of my question with this video from an Avicii livestream: https://www.youtube.com/watch?v=EEcq4sXN7jQ
From a business perspective, the only way you get royalty payment on a song is if you have a portion of the writer's credit. When the money for plays is given to the publishing right's organization that collects it, they allocate it into 200% - 100% that goes to the publisher (either you or, more likely, your record label) and 100% that is divided equally amongst all the writers.
For your typical pop song, 50% of the writer's earnings goes to whomever wrote the lyrics, and 50% goes to whomever composed the music. That can get divided differently based on genre, song, and who wants writer's credit (except for the drummer, cause drummers get shafted on writing copyright).
Could be that a lot of those people are just trying to earn a little bit more sustainable revenue. Also why it's a good idea to start collaborating early and often, given you don't just work with any old producer that walks in the door: the more songs you have published with your name on the credits, the more opportunities for pennies, nickels and dimes to accumulate from radio/streaming plays and visual media synchronization and good old fashioned direct downloads.
And that last one might not stick around much longer.
