But the majority of songs (not just Top 40) are about love. I'd say 80%, if not more. Up until "
Immigrant Song",
Led Zeppelin hadn't written a song that wasn't about love, romance, or
squeezing someone's lemon until the juice ran down their leg. Almost all of the
Beatles' early stuff is about love ("She loves you, yeah, yeah, yeah!"). There aren't too many lyricentric bands who don't sing about love.
It's all about how you write them, though. All it takes are some interesting lyrics and a catchy hook and you've made the song interesting. But that's too much for some people, so they imitate Smoove B, add 12 slightly different thumping bass beats, and sell five million albums. Look at Boyz II Men. If you removed the words "I", "you", "girl", and "hurt" from their songs, you'd be left with nothing but Nate, Mike, Shawn, and Wanya in the background singing "Ooom" and "Aaah".
Maybe I shouldn't pick on Boyz II Men, because there are a other groups guilty of creating music a hundred times worse. But you see the point, no?