It really boils down to the same as pretty much any other market or hobby: supply and demand.
The Metallica shows are at a stadium. If you think they are overpriced, just watch ticket prices. They routinely drop prices if shows aren't selling, and the same can be found on the aftermarket like Stubhub etc.
If prices don't drop, well, tough titty, guess you'll just have to stay home that night.
It doesn't really bother me either way, I buy tickets to shows I want to go to if I think it's worth it. Just like anything else I spend my money on.
What cracks me up is the once every 10-years thing when it suddenly becomes news. Some Senator can't get tickets for his daughter for Taylor Swift? Issue a press release and start an investigation! Where was this guy when I was trying to get AC/DC tickets 15 years ago!? Nothing has changed.
In the end, you'll never make everybody happy. Nobody is entitled to a Taylor Swift ticket. She's playing 60,000 seat stadiums. If 400,000 people want tickets to the show, well, do the math. That's not Ticketmaster's fault.
As far as the specific example posted - $960 for four good tickets to Metallica (it's a two day ticket) doesn't seem too outrageous to me. That's $240 per show per ticket to see Metallica. Perfectly fair value in 2022 to see a huge band like that (if a little on the cheap side). People always gripe about how they saw Metallica in 1984 for $12...I mean, how much money were you earning in 1984? What percentage of your net worth was $12 in 1984, vs. now? How much more does everything you buy cost today than it did in 1984? It's not 1984 anymore.