This is purely anecdotal but when I was in high school the demos that listened to rock after whites were the Asians and Hispanics. A lot of bands had Asian and Hispanic members, sometimes they were even the singer. Rock had a universal appeal to it though especially with the Hispanics it was treated as an interchangeable genre with pop and such.
I feel like the schism that happened in the early 10’s hurt not just the rock formats but did a number on the audience. But it particularly hurt Alt as they chased the quirky pop songs while a lot of the listeners, young and old alike, just wanted to rock.
Part of it is also marketing. The labels prefer to push beat-heavy solo artists. There’s only one person they need to pay. Even quite a few bands are essentially one guy who hires touring members like Tame Impala. You don’t need to pay touring members royalties!
WNYL was probably still salvageable, KVIL was doing even worse in the Dallas billing and they bounced back. But KVIL took advantage of a unique implosion by a rival station to take their listeners. WNYL would have had a tougher and longer road to recovery.
I think someone will try Alt again in NYC. It’s probably the most viable rock format for the city as Alt tends to be more diverse in its offerings compared to Active Rock and AAA. (I am saying in terms of sound not race, though there have been a lot of black artists charting on Alt the last couple of years). I think if someone has a better plan than what Kaplan had we could see it be tried again, with better results.