More seriously, whenever I ask a young person on public transport to use headphones (and luckily I live in a region where I can safely do that and enjoy some authority as an older person), the response is usually that the youth doesn't have headphones on him for whatever reason (doesn't own any, left them at home, whatever). But with the breakdown of this taboo, people don't feel that not having headphones should stop them from sweet TikTok dopamine.
If from the start they had simply had separate volume controls for alarms / phone calls / media / alerts then I think this would not have become a trend.
What you experience is a cultural difference.
In that not all cultures recognize causing negative externalities as a bad thing?
if you want someone to respect your feelings then ultimately you will have to make them. for broke-ass hoodrats, for whom economic factors won't work, that means eventually going to Louis' ultima ratio -- e.g. calling this out may lead to a fistfight on a moving bus.
Disapproving glances on the subway when their music is too loud does not rise to that level, however.
I was that shameless annoyance once too. It doesn't mean shame is dead.
I noticed olders are more ignorant too:
* Standing prolonged in the way during smalltalk? Even 60y+ seems to have lost the art of stepping aside as much as possible.
* Stopping a crosswalks, esp. when children are waiting? 50y+ seem more prone to just driving ...