This film's secondary protagonist was a teen girl. It makes sense that there were would be catchy pop songs, since that's a huge part of her world (just as construction, police and superheroes were a big part of the first film because they were a big part of young Finn's world).
That's the point. The whole scene is a brilliant critique/satire of alternative therapies, modern pop music, idyllic Pleasantville-style 60s suburban America and probably some other stuff that I'm missing.
On top of that, the scene has some really fun visuals that I love (Batman flossing, the chase through the dollhouse, Wyldstyle climbing the volume bars) and killer lines that crack me up every time ("my leg is a piano", "don't listen to the music if you want your noodle to stay al dente").