If I wrote a song, I can imagine that I'd only want to perform it at the time that I wrote it.
You really give something of yourself away when you write songs, poetry, or anything really.
To be asked to turn around and perform something that you wrote years ago, when you thought or felt differently to how you do now, must be pretty hard.
I wonder how many times a singer, or actor, etc. has refused to perform a song, (or whatever) because they said something that they don't feel is appropriate anymore.. because their circumstances have changed, or because the political climate has changed, or because someone has died, etc.
Maybe that's why there is the 'author' and the 'performer' set up, so that the emotion is kind of decoupled from any particular individual, and someone just picks up a 'persona' to hide behind.