Why do people like to watch shows about SINGING?

And also music is about the easiest thing to sell, just ask disney.

Yeah, make sure to ask the RIAA/MPAA as well.

Singing is easy. Many people can do it, and it allows for a reproduction of talent. Although American Idol is a talent show per se, the ones that have gone on to win it all have all (or mostly) been singers. A singer can come back to do different songs time and time again. It's much harder for people with more esoteric abilities to come back with something fresh every time.