Because fuck you, that's why.

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.