Why does rock concert sound suck?

There are many reasons rock shows generally can sound awful. For one thing, and the most important one is that most of these arenas are not designed for sound quality at all. They are echoey, sound smearing, godawful places of zero acoustics.  All the DSP in the world isn't going to tame that mess. 

In such venues, the best that can be done is to make the show an "experience" with tons of body shaking low bass and a light show to blow your mind.

When you go to a show you aren't paying to see someone in a recording studio. If you get lucky and your band is playing a quality hall, say where a symphony orchestra plays, or a smaller theater with some sound treatment on the walls, you are lucky.

I've seen countless shows over the last 45 years, and the sound quality has run the gambit from great to crap. 

My favorite venues are either outdoor ones that don't have echoey sound or smaller indoor venues having 200 to 2000 people. Think bar shows up to modest venues. They seem to offer your best chance of hearing good sound. 

For instance, over the last 30 years I've gone to an outdoor music festival of Americana/Rock/Jazz/Bluegrass called Merlefest. And the sound there is GREAT, mainly because those running the soundboards actually care. 

Lol a friend and myself went to a bar that had an Irish  band playing for st Patrick s day. On there break asked if they would like us to setup the system  a bit better they said sure asked us what we knew about it told them we were both audio files  and it was a life time hobbie we got the speakers close to equal distance  from the wall leveled them somewhat close one was at leat 2 feet lower than the other did a few basic things they started to play the first song and stopped mid song and thanked us. After the show they offer us a job!!! Lol had fun that night. 

Sound men start with the drums, getting a great-but-too-loud sound from the kit.  Then they do the same with the bass.  After that there's nowhere for the higher pitched instruments and vocals to exist.  And it all sounds like crap.

My wife and I were once at a Los Lobos outdoors show and the sound was so bad we decided to go home.  As we were walking away we hit a point where the sound was decent enough so we sat there and stayed for the rest of the concert.  So it can be a relative thing.

The most painfully loud band I ever heard was the 13th Floor Elevators at the Safari Club in Baytown, Texas ca. 1968.  This was long before big PA systems so I'm not sure how they managed to do it.  Small room, I guess.

I’ve become very picky over the venue choice v. the performance to be attended. Leaning towards smaller halls, outdoor venues, and who is headlined and what they do....

Larger venues, esp. outdoors, draw fans that either spend too much time on a cell or loud chatting with whomever you came with. Esp. with the $ for even a mediocre seat (tending to under a balcony or nosebleed...

The cheers/yowling of the audience is my downfall, the 'beige racket' typically louder than the flown drivers on stage.  I've literally had my ears go 'pop' and toss the towel.  Between that and loud machinery, my hearing required earplugs, later aids for just the day by day...

I’ve been to enough concerts over the span to ’who/where’ determines go or no go.
Overall, it’s served me well...but I still take 3 earplug pairs with me:
Vibes, a ’high fidelity’ version which knock Everything down 15 dB, or...
Hearos, a ’roadie’ plug from Guitar Center. Attenuation varies with fq, 2.7 to 4.9,
’Shop plugs’, used in our wood shop, that slam the door on everything (great ’escape’ plugs, last used for a Dave Matthews gig in a basketball bathtub...worst ever of his attended...spouse is a fan of the ’early’ stuff...)

Fortunately, more good than awful. The occasional ’flawless’:

Paul Simon, Cyntia Woods Pav., north of Houston. Terrific thunderstorm prior to and delaying the opening of the set, we watched as the front rolled in, soaked Everyone (we had grown a brain, rented chairs and brought a tarp (had noted the forecast and the radar...). Opened with ’rainforest noodling’, perfect choice that brought cheers...
Same venue, The Blue Man Group to a 33.3% crowd, the Complex Tour. (A lot of which is on YT; ’I Feel Love’ w/Venus Hum vocal is a good example). More percussion horsepower imaginable handled nicely. And just f’n Fun...

Talking Heads~David Byne: Previous at the Greek Theatre, Berkeley, Byne twice right here in AVL, small hall. Both times, front row balcony dead center. Pefect.
First tour had a player on a Stroh violin, which went great with what was being performed. Second tour had St. Vincent as guest vocalist on some of her ’compostions’....

Others: Anything Bill Graham had anything to do with back in the Bay Area.....within ’practical limits’...

I suspect all had their own mix crew, sure sounded that way...

Over the last decade or so, about 90% of the concerts I've attended have had atrocious sound.   I just don't go to many anymore...bad sound damages my ears; bad sound is unpleasant; bad sound prevents me from hearing the artistry that drew me to the concert in the first place; bad sound wastes my money and my time.  I've never understood why a band would carefully craft an amazing sounding album and be content with lousy live reproduction of it.