I can't help thinking some of this increase in repetition is down to the change in technology over the last 15 or so years. I'm willing to bet that every song in the top 20 is produced using a computer now. And the one thing computers can do that tape can't is repetition. You can copy/ paste that mutha till your heart's content.
I have a feeling this mainly happens during the demo/ scratch stages of production, but if that version is what gets the suits approval, that's the version you're going to polish up into a complete production.
No evidence for this, just a hunch...