Frogman, Nancy came out in 64; the country was in a vastly different world musically at that time, and that determines the music that's chosen and gets played.
No matter how good the musicians and their music is, the public at large chooses whether or not it gets played and noticed. I'm going to select music from the mid 60's to illustrate where I'm coming from.
https://www.youtube.com/results?search_query=dusty+springfield+the+look+of+love
Carmen McRae; "Alfie" in 65 was a popular tune, that fit the description of "Our music";
https://www.youtube.com/watch?v=5ozYKIWfRpQ
Nina Simone; "Feeling Good", sure made me feel good;
https://www.youtube.com/watch?v=oHs98TEYecM
I could go on all day in regard to music in the "Mid 60's", but you get my drift. What I'm saying is the same thing you said; there are terrific musicians every year, the top music schools are still open; it's the public that determines what we hear.
There was a local establishment that I went to every week end that incorporated an African Finger piano, that sounded ever so good to me and the people who went there; but when that establishment folded, never again did I hear that kind of music.
If the best jazz band ever, played in the boonies in Indiana, we may never even know of their existence. There was a club called the "Tanganyika" that was in "Columbus, Indiana" that I went to in 64, and the club over flowed with people from surrounding towns, because there were not enough people in Columbus to support that kind of attendance. As good as that band was, I don't remember the name, and they never made it big.
If you just let Carmen play for awhile before you go to the next link, you will hear some of the best of Carmen.
When you get to Nina Simone, do the same thing, let it play. The point I'm making is that the "Mid 60's" was an incredible time for music.