Why does rock concert sound suck?

The larger the venue is, the worse it will probably sound. When you add in the stratospheric prices at most of the larger venues, this is not a good mix.

Learn where the good sounding venues are in your area and support them. In the past year I've seen King Crimson, The Ocean Blue, Gang of Four, Steve Hackett, Joe Jackson, China Crisis and Norah Jones. All of them were in good sounding venues and the cumulative ticket price of those shows was far less than what a ticket would have cost me to see Elton John or Van Morrison when they recently passed thru town

I never thought that it would happen, but I LEFT an Elton John concert right at the beginning! Loud was not word for it. Jet engine loud was a better description. I could feel the MIDRANGE bouncing off the wall. Too bad.

 Went to a YES concert many years ago. It was nearly perfect in spite of the fact the concert was at a multipurpose venue. Never a good sign.

 Last concert was a cover band for Led Zep. Completely incredible, and not damaging. High level of talent there. Was very surprised.

I was once at a concert by the Cars, on the Panorama tour, and of all bands, this was one of the loudest I'd ever heard - the PA was blowing the hair on my head and punching me in the gut and blasting my ears!! Yes, Grand Funk did that once to me in the early 70's, but this was the CARS!

But I think a lot is down to the sound crew - there are some venues I've been at a great many times, and most bands sound excellent, but a few bands sound as atrocious as can be in the same venue. 

But then there are bands like the Grateful Dead who always put big, big emphasis on sound, back to the days when Owsley Stanley was their extremely innovative sound man. I've heard the Dead sound superb in all kinds of venues, inside and outdoors. 

A lot has to do with who is running the mixing boards I have heard 3 bands at one concert and the speaker setup used and most important the mixer board  to set the 

tine ,i have  seen some have a person on the floor and relaying , and others juston  stage what they think is best, mixing is an art in itself .

I’m a decades long pro musician (basically retired now) and small venue live sound mixer. Most people have absolutely no idea how modern sound systems work, including claims of "electronic manipulation." Huh? You mean EQ? The mains mixer has all the control, and it’s up to that person to make things sound good. Go to a concert at the Berkeley Music Hall and see things done right...I avoid large shows mostly because of dumb crowds and bad sound, but sometimes we get invited to something like a few years ago seeing Steely Dan (with Becker) with Elvis Costello opening at some gigantic outdoor thing in Boston...sounded great. Paul Simon and Sting at the Garden from a "box" sounded great...Jeff Beck some years ago at the House of Blues with perfectly balanced sound. So hey...good things CAN happen. Talked into going to the last day of the Newport Folk Festival a while back and the sound people must have been asleep...inexcusably bad sound at a legendary show...Gillian Welch played her first couple of songs, and note these guys use 3 mics or something, and she had to ask the sound people to turn on the guitar mic of the brilliant David Rawlings...man...I could go on and on and on...wait...I just did.