Much of the music from the 60's is long lost in our memories (ditto the 70's). We remember the good stuff, or more specifically, we remember the stuff that generates the highest emotional engagement, which does not need to be the highest emotional engagement in everyone, but a high enough emotional engagement in enough people to keep the memory alive:
On the other hand, if you take away the recency effect it’s hard to see which albums from the last 20 years will make the cut a century from now.
I copied a list from Wikipedia of the top songs of 1969. How many of those do you remember clearly? "I can't get next to you" by the Temptations I had no memory of. Same for "I'll never fall in love again". "Sugar Sugar", "Everyday People" .... will never forgot those songs, and can sing word for word. They generate strong positive emotions. It was a particularly good year though. Go to a bar and watch what songs younger people are emotionally engaging with when played. Those will last.