Hm… I think that’s more of a medium thing–in that, music and singing is frequently included in children’s cartoon, whereas a written fic could just do these are character thoughts directly–and a SU specific thing because Steven was raised by his rockstar dad.
I mean, you could very well imagine the gem-ified Team Seven singing if you like, but I don’t know how I would write that in a fic without it getting cheesy.