The issue of how hit songs are made has been mentioned tangentially. They aren't made by bands; they're made by producers. This is an excerpt from a story called "The Song Machine" written for the New Yorker by John Seabrook back in 2012. I especially enjoy the part where two different singers make two different songs out of the same backing track, and nobody really notices.
Most of the songs played on Top Forty radio are collaborations between producers like Stargate and “top line” writers like Ester Dean. The producers compose the chord progressions, program the beats, and arrange the “synths,” or computer-made instrumental sounds; the top-liners come up with primary melodies, lyrics, and the all-important hooks, the ear-friendly musical phrases that lock you into the song. “It’s not enough to have one hook anymore,” Jay Brown, the president of Roc Nation, and Dean’s manager, told me recently. “You’ve got to have a hook in the intro, a hook in the pre-chorus, a hook in the chorus, and a hook in the bridge.” The reason, he explained, is that “people on average give a song seven seconds on the radio before they change the channel, and you got to hook them.”
The top-liner is usually a singer, too, and often provides the vocal for the demo, a working draft of the song. If the song is for a particular artist, the top-liner may sing the demo in that artist’s style. Sometimes producers send out tracks to more than one top-line writer, which can cause problems. In 2009, both Beyoncé and Kelly Clarkson had hits (Beyoncé’s “Halo,” which charted in April, and Clarkson’s “Already Gone,” which charted in August) that were created from the same track, by Ryan Tedder. Clarkson wrote her own top line, while Beyoncé shared a credit with Evan Bogart. Tedder had neglected to tell the artists that he was double-dipping, and when Clarkson heard “Halo” and realized what had happened she tried to stop “Already Gone” from being released as a single, because she feared the public would think she had copied Beyoncé’s hit. But nobody cared, or perhaps even noticed; “Already Gone” became just as big a hit.
A relatively small number of producers and top-liners create a disproportionately large share of contemporary hits, which may explain why so many of them sound similar.
edit: one more juicy bit--
Whereas rock is about the sound of a band playing together (even when its members aren’t actually together) and features virtuoso solos played on real instruments, today’s Top Forty is almost always machine-made: lush sonic landscapes of beats, loops, and synths in which all the sounds have square edges and shiny surfaces, the voices are Auto-Tuned for pitch, and there are no mistakes.