If I knew a gig was going to be phone and superwatch free, I would totally try to go. Even if I didn't like the music that much. Just to remember what life was like, when it was proper, and people weren't continuously seeing through a view-finder what's right in front of their eyes.
One reason I like classical concerts is that people are, on the whole, more cerebrally refined than other music genres. (Yeah, bite me) They want to be there in the moment, absorbing the acoustics, and the finesse of the musicianship in finite detail. You can actually close your eyes, and not only still be there, but you can be MORE there...trying to compress a full live symphony orchestra and choir onto a mobile phone is bound for disappointment.
We're usually older at these classical music gigs, and recall life before the mobile revolution. We just lived it. But there's also a sense for the younger people of getting your money's worth, and if you CAN record your life's most expensive memories, then why wouldn't you? If I'd paid thirty squillion quid for a Taylor Swift ticket, you know I would want to film at least some of it. And steal the seat. And nick some commemorative toilet paper. And a bar mat.
This is why I'm not allowed in nice places any more.