Why does rock concert sound suck?

Coffeehouses and small venues are to my liking. Who needs hearing loss? I got on the board of my local coffeehouse some years ago just so I could get my mitts on the tape library. GREAT STUFF! 

That is one of the biggest reasons I walked away as fast as I could from Rock-n-Roll early on. In the 30s through the 50s we had a lack of high quality electronic equipment to work with then somewhere in the 50s we discovered dedicated sound engineers. They were mostly self-taught and not well versed in sound. They all had their own idea of how things should sound.  Thus we had to get creative with our listening environment by utilizing things like Graphic Equalizers. Though today there are actual schools teaching sound engineering, much of it is left up to the individual. Many artists have their own Special guy that they will used and who travels with them, then there are others who depend on the house sound man or a locally hired sound man hired by the promoter. We have much the same problems with the gear used. Even when I first traveled around with an early garage band doing their sound, though we brought our own gear, we were DICTATED to by the club owners or property management as to what we were allowed do with the sound. Ironically I have to agree with @dpop and don’t want anything in my system to colour or alter the sound but prefer to hear what the engineer heard and try to get into his mind. He was as much responsible for a Band or groups sound or style as the group.

I've always preferred club venues for sound quality.  No, you won't see U2 but back in the day all the cool indie bands played the clubs.

Now? I can't stay up late enough to even see the opening act.  A few years back I had tickets to see Killing Joke.  I figured I could see at least a few songs before sneaking out to head home to bed. Called the venue to see what time they'd be on, and the answer was "some time after 12:30."  OK, not gonna be awake at that time.

I know it's not rock'n'roll, but hey it's the music of the older generations now, not the children, and it would be great if there were more early shows. 

The reason is nothing is analog it's all digitally processed. From the mic feed to the board the amplification many layers of processing are going on stripping the soul out of the music. But there is a bit of a rebellion going on younger guys are buying vintage PA gear and running a less processed setup.