I agree with MR BK about audiences today....and I am unanimous in that.
I think it started sort of with the tv show STAR SEARCH.....each of the singers had 45 seconds to do their thing.....and at 30 seconds, each of them would sing a loud high note or start yowling and growling and the audience would always respond in kind - prompted, I'm sure.
It continued on American Idol, etc.....and still goes on.... It makes me want to avoid theatre.