There are likely many reasons, among them the fact that the invention of recorded sound made listening to music something you could do alone in the first place,

There are likely many reasons, among them the fact that the invention of recorded sound made listening to music something you could do alone in the first place, and the general trend of individualization in the Western society in the 1900s. When it comes to partner dancing, there exist modern social dances that can be danced to a wide variety of pop music, mostly descendants of the original 30s/40s swing dances like Lindy Hop and Jitterbug, and even moreso than those predecessors, emphasize improvisation and nontraditional lead–follow dynamics. West Coast Swing is probably the most popular example while by no means mainstream; partner dances simply aren’t that fashionable even if there has been a resurgence of some sort in the past decades. (Coincidentally, I happen to be currently in Budapest, at one of Europe’s largest annual WCS events!) Of course, there’s the fundamental fact that solo dancing requires next to no skill, while acquiring even basic partner dancing skills requires one to take a class, or at the very least ”learn by doing” in an appropriate environment.