Interesting post by Al which finishes I always felt if we don't leave footprints in the sands of time - no one will know we existed.
My reaction to what he has said is that some songs are transitory and some of those are meant to be; others have a timeless quality. In the days before recorded sound, it was only the timeless ones that survived. Marxists would say that they were taking up the "the folk".
Songs like Tom Paxton's Lyndon Johnson Told the Nation, hugely popular at the time have little relevance in this age, but when I sing a Manchester broadside song from the 1840s Old England, What Have You Come To? though in it the references are from 180 years ago, the commonality with our current political and economic woes are obvious and I can see that audiences relate to the hardship and inequality that the song portrays.
Of course, since the days or recorded sound all songs survive in some obscure places.