It just makes dealing with incessant city noise so much more manageable.
You don't even have to be listening to music.
But if you are listening to music, you hear it so much more clearly and can use a lower volume.
From a quality of life perspective, if you commute by foot/subway/bus, they're so so worth it.
(Yes there were noise-cancelling headphones before, but always bulky or with wires. With AirPods, they're just effortless to bring+wear.)