As a record collector who grew up in the 60's and prefers 60's rock, along with big band swing era music, a record dealer told me today that customers are simply not coming in looking for 60's rock, other than the usual stuff, like The Beatles, Stones, The Who, Dylan, etc. He also said nobody comes in looking for swing era big band records either. Of course, this dealer specializes in heavy metal and punk rock.
I think it has to do with the passing of generations. The WWII swing era generation is practically all gone, the 50's doowopers are dying rapidly, and now, the Baby Boomers who liked 60's rock are starting to go. It's inevitable, the circle of life.
Gettysburg will always have a fascination for people as the largest battle and the turning point of the war. Interest is bound to ebb and flow. Those of us here are hardcore CW people, but the average Joe & Jane are not, and most young people couldn't be bothered, in all honesty. That's troubling, but I hope Gen X-ers and Millennials will gain an appreciation as they get older. I didn't care much about CW history until later in life, when I became obsessed with it.