Lady Gaga is prob not a good example since she writes or has a big hand in writing pretty much all her songs. Like most pop artists she utilizes producers and songwriters, but she relies on them less than say Rihanna who essentially has had all her hit songs written for her (or picked up songs originally written for other singers).
There was once an article about a "songwriters auction" where songwriters would pitch their music to producers of famous singers. (sorry can't find it now)
For most commercial pop music it's an assembly line really. Several stages specializing in one thing. McD ideas for McD music. Tastes the same as well.
The pop-music assembly line is actually pretty fascinating -- and definitely staffed by artists. Check out this New Yorker article about Ester Dean, whose role on the assembly line is coming up with a hook for the producer's computer-generated tracks:
Dean has a genius for infectious hooks. Somehow she is able to absorb the beat and the sound of a track, and to come out with its melodic essence. The words are more like vocalized beats than like lyrics, and they don’t communicate meaning so much as feeling and attitude—they nudge you closer to the ecstasy promised by the beat and the “rise,” or the “lift,” when the track builds to a climax. Among Dean’s best hooks are her three Rihanna smashes—“Rude Boy” (“Come on, rude boy, boy, can you get it up / Come on, rude boy, boy, is you big enough?”), “S&M” (“Na-na-na-na COME ON”), and “What’s My Name” (“Oh, na-na, what’s my name?”), all with backing tracks by Stargate—and her work on two Nicki Minaj smashes, “Super Bass” (“Boom, badoom, boom / boom, badoom, boom / bass / yeah, that’s that super bass”) and David Guetta’s “Turn Me On” (“Make me come alive, come on and turn me on”).
I mean, sure it's ridiculous, but these tracks are made by people who are uniquely good at the ridiculous things they like doing. If they've found a way to get paid for that, my hat's off to them.
So I guess this explains how Justin Bieber's 'Baby' has so many songwriters/composers. It's really an assembly line
"I mean, sure it's ridiculous, but these tracks are made by people who are uniquely good at the ridiculous things they like doing. If they've found a way to get paid for that, my hat's off to them"