Several reasons.
First, the equipment used is vastly better. The speakers we used back then were basically piled-up experiments. We’d try different things, but we didn’t really have the test equipment to do proper experimentation. Every sound company basically built their own speaker cabinets, or bought random components from various manufacturers - EV bass, JBL horns, etc.
Current speakers are supplied by manufacturers as complete systems. The handful of sound companies that build their own are so large that they qualify as manufacturers (Clair/Showco). Pretty much a tour can specify a particular speaker system and be able to get exactly what they wish anywhere in the world. And that speaker system is vastly more reliable, as well as vastly more efficient. The days of 20 trucks hauling speakers, staging and lights are long gone. The speakers to do an arena these days are expected to fit on the raised floor portion of a single trailer, aka the “dance floor”.
Oh, and the speakers are far more controllable. During the show, you might notice someone wandering around with a tablet. They are tweaking levels of different speakers in the stacks. It is no longer necessary to blast the folks in the front to reach the folks in the rear - the speakers intended for them are blasting away far above their heads.
Second, in-ear monitors. These are really high-zoot earphones custom molded for the wearer (that can cost upwards of $1000 a pair). These replace the stage monitors. The advantage is that by putting the sound directly into the ear of the performers, they are able to hear themselves and the rest of the band much more clearly. Also, the stage monitors would have to be loud enough to overpower the sound of the main speaker system echoing back to the stage. That set a minimum level of the sound system. With the whole band on IEMs, the stage gets dramatically quieter. Oh, and by the way? Those piles of guitar amps were bullshit. Ted Nugent had fake amps made, and only one pair was real - it was the one that had a microphone on it. The current trend is to lower the noise level on the stage even more by locating the guitar and bass amps in sealed boxes off stage, unless the player uses feedback and needs the cabinet there to play off.
Third, mixing boards have improved even more than the speakers. Virtually all tours use digital mixing boards that allow the sound engineer to save and recall any changes to the board settings. They’ll even record every track of every show to a computer, and play back last night’s show to tweek the sound system - the band is not even needed except to make sure they are happy with their instruments. And the board has vastly more adjustment power than any sound company had back in the day. If you wanted a compressor to control the dynamics of a channel, you had to wire one up. But a new digital board has compressors on every channel that are far better than we could carry. If the engineer has a specific one they prefer, they can buy a software version of it that loads into the board. No loose screws, no ground loops, no bad capacitors.
There are many other things. Digital “snakes” so the tiny voltage coming from the microphones don’t have to travel hundreds of feet to the back of the room. Vastly improved monitor mixing systems so the musicians can hear each other better (which usually means they play better together).
I’m sure there are plenty of others, but it’s late.