It's definitely a weirdly fascinating thing to ponder. I found
this book on the subject; I tried to find some excerpts online but there aren't any, sadly.
Also found this:
Attention K-Mart Shoppers | MetaFilter
Apparently someone took it upon themselves to digitize various 1980s-90s Kmart playlists.
(Finally!) Most of it is just bad 80s pop but it still may be worth sifting through.