[smeyer]

And yet, I've been to plenty of venues that were uncomfortably loud in back while not going to any (indoors, professionally set-up) venues that were uncomfortably quiet in back.

I think it's more than what you've described. I think it's that a lot of folks actually prefer dangerously loud volumes, and this contributes to a positive feedback loop of expectations for loud concerts. I wish most concerts were quieter, but I may be in a minority.