Because metal is not just "stuff with tons of growling and screaming in it", Cannibal Corpse are death metal, Gorogoroth and Dimmu Borgir are black metal. Three metal bands don't represent everything about metal
There are tons of different subgenres of metal, Symphonic, Doom, Thrash, Folk, Progressive, and so on. A lot of metal bands have singers who use "clean" vocals.
Try listening to these bands, maybe they'll change your mind about metal:
- Epica (they have a back-up singer who does death growls, but their lead singer sings clean)
- Dream Theater
- Judas Priest
- Rage Against the Machine (they're not "pure" metal as some would say, they have rapping vocals, so it's rap-metal)
Metal music is also much more deep and requires more thought to interpret than disney pop, not to mention it covers a wide variety of topics. For example, Dream Theater writes many songs on philosophy, human emotions, and the meaning of life. Many metal bands, such as Ensifeurm, Amon Amarth, Iced Earth, and even Iron Maiden write songs about mythology and fantasy, which have a lot more meaning than any disney pop