In a word: amplification.

The children born after the beginning of the rock era are now in middle age.

For their whole lives, they've been listening to live music at such volumes that you could yell at, much less talk to, the person next to you, and no one else would notice. They just have no idea how to act when any kind of live performance is at volumes below the pain threshold.

Go to some performance where the whole audience is in late middle age or older, and see if you don't notice a big difference.