As yet another kid, having spent far too much time on the Forum moaning about other kids, I would be inclined to agree in general, but I do think your post is something of a generalisation. Lots of the people I've noticed doing it are 20- or 30-somethings, although to be fair this is probably more indicative of the general demographic of my area than anything else.
Disagreements of various kinds regarding acceptable noise have been around for generations. I know people who can do anything with ambient noise coming from the TV, and people who can't concentrate at all with it in the background; people who are perfectly used to whistling such that they tune it out (or, like me, start whistling without realising
), and people who find it horribly piercing.
Not just "this" generation. In my experience, it's a sizeable amount of the under-50 population. I hate loud environments almost as much as I hate social engagement, so I guess I'm an outlier! I don't have, let alone use, headphones - if I want to watch a video or listen to some music, it can wait until I get home, and I'd far prefer to listen for announcements anyway - so clearly I don't think they're a prerequisite for modern life, but I can never help but wonder whether it would, in fact, be worth it to block out all the inane noise. Usually, I discount this in my head for three reasons. I can't deny that some of the loud conversations I've overheard on trains are highly amusing - my favourite is the person trying to convince his (grown-up) daughter that the ferry from North Shields to South Shields also goes from South Shields to North Shields! Also, in my experience, headphones only make people louder when they do talk, as they struggle to hear themselves through them. Thirdly, and perhaps most importantly, I've given more than one person help and/or advice because I've noticed their predicament (unable to open door, trying to use the Tube to get to Ipswich, etc.), which I wouldn't be able to do if I was absorbed in my headphones.
A phenomenon that has existed in many forms for as long as there has been cultural change, in this case exacerbated by, in my opinion, people losing their situational awareness during COVID.
I think it's a perfect storm, to be honest. I think part of it is the trend in short-form videos with attached "music", coupled with the pandemic, coupled with a general rise in discourteousness among people of a larger age range than one might think. If someone is playing "music" out loud on a train, usually I don't intervene - I'm not going to change anyone's mind - unless they're already sitting right next to me. But it's not just music - voices are routinely raised to far above acceptable levels, there are loads of drunken football fans singing and chanting (always a nightmare, and in 99 times out of 100 worse than the kids playing "music", which is, at least, slightly more likely to have a tune), and, in terms of other anti-social behaviour, vaping is rife (again, not always kids), feet practically live on seats, and queuing can be disorderly, although I think less so in commuter-belt country.
One incident in particular sticks in my mind whenever I'm thinking about this problem. I was boarding a train with a short turnaround at its terminus, and, as I got on - the first on the train - through one door, I heard a loud shout from the other door in the carriage, along the lines of, "Oi! Have some manners!" or words to that effect. The shout was closely followed by a teenager, and then the owner of the shout, who was, I would guess, in his fifties. I could guess what happened - the boy had clearly pushed past the man in the rush to get on the carriage first, or something similar - the doors are wide enough to fit two people through side-by-side. I would have thought nothing of it - apart from the fact that, as the train pulled in, people strung out along the platform, I had spotted the man who had shouted, who was originally standing a few feet to my left, reach out for the door button on the penultimate door and walk down the platform, in step with the train, with his hand on it. If I had been standing in the proper position for that door, I know what I would have thought of such behaviour. Trains - especially commuter trains - are seen as being these boring metal tubes that get you from A to B and give you however many minutes of doing nothing, a bit of time to yourself before the long grind of work. Some time in your own little world.
I think that rather insular mindset, above anything else, is the root of the problem.