Tastes change, and youth today like Pop and Hip Hop artists... There's still plenty of money in music, for example Taylor Swift sold multiple dates per city with tickets nearing the $1k range per seat. Adele's latest album sold 5 million copies in 3 weeks. It's all manufactured music at this point anyway, primarily teenage-early 20's girls singing 3 minute songs with a hired background band containing no more than 30 seconds of non-repeating content. Catchy but transient tunes.
Clearchannel contributed to rock's demise when they bought every radio station in the United States and the few rock stations still allowed to play rock are stuck with decades-old top-40 rock in tight rotation... is anyone interested in listening to the same 3 songs from Nirvana's catalog every single day for the rest of your life? I was tired of them when they were still making music. Metal is relatively strong but remains low key as there are no stations (and never were) willing to play metal, nevermind the demise of MTV whose execs decided that it's too hard to count ratings with videos, so they have other content. Now my dial is stuck on a Hip Hop station for the variety, and I have to spend a fair amount of time and money to track down lesser known contemporary metal bands. The good news is that older metal bands find it worth while to continue to make music and tour, and it doesn't cost Taylor Swift money to see them.
Kids hardly know that pinball exists, and have no real attachment to artists with throw-away music, so no modern artist/band fits the mold. Enter super hero themes... kids dig them, so it works for pinball.