Some time ago I came across a description of how traditional song gets passed on in Hungary. You don't find old people learning songs in their childhood and then amazing the audience with the same ones 60 years later: instead, there are different repertoires for each age group. You sing the songs that are appropriate for your own age, after learning them from singers not much older than you are. (To some extent you get the same phenomenon in other places, even the UK for some kinds of song).

Advantages:

- you get to keep learning new stuff.

- you don't need an enormous memory since collective memory is working for you.

- nobody complains that your old material was better.

- the old-singer's music you get to do near the end of your life will suit an old person's voice and performing style.

- you don't get to bore your audience rigid by singing about issues that only mattered before they were born.

- songs written 40 years ago that nobody but the songwriter had any time for don't get rehashed, since the songwriter themselves would be too embarrassed to publicly perform a song that only made sense to the 20-something they once were.

The idea that one man with his guitar gets to create songs for the ages that the world will want to pay to hear for his entire career is usually just plain delusional. Almost all singer-songwriters can expect to wake up one day as failures at best, grotesques at worst.