That age group is pretty large, though. So many people had walk-mans in the 80s and 90s. I'd also venture to say most people who would go to a rave probably like music enough to own headphones.

I do agree though, the useage of Spotify as a given is annoying. Especially since everyone will never be perfectly synced up. I remember silent raves, back a decade ago, would use a FM transmitter mixed with cheapo portable fm receivers.