I like to ask myself this question sometimes, as a self-reminder.
In my mind, sheet music was invented to help us recall more and more difficult music. The sheet music isn’t the music, it’s a short hand for us to be able to sing or play the music well.
Certainly, composers have since used that shorthand to create ever more complex music – music that couldn’t possibly be learned and performed without paper and little blobs of ink in front of us.
But even so, the music itself lives somewhere beyond what the paper can touch. The paper helps us learn it, helps us remember it, helps us analyze it. That’s what it’s for.