Why is song-writing the one genre of creative writing where it is expected to be about you?

Aside from autobiographies (which might only sometimes be considered creative writing), there aren't really any genres I can think of that are about the self as much as music is. This is weird because it is my understanding that most people (me included) generally dislike when a story being told is obviously about the author.

Essentially every song I hear is about the person singing it, or perhaps their relationship to a person close to them. Even just writing a song from the perspective of another is considered going above and beyond alot of the time. To be fair, this could also be a more modern thing, or I could just happen to only listen to self-centered music.