Haven't read all of the thread, but I think it is a combination of different things:
1) School is harder - the curriculum is old fashioned and doesn't actually prepare young people for the realities of modern life, school behaviour policies are more interested in creating little automatons than encouraging mutual respect and preparing young people for independence and the lack of inclusivity and recognition of differences play havoc with children's mental health - not just those that are ND but also those that are NT but who don't fit into the box we expect young people to fit into these days.
2) Parents are less likely to push their children to find part time jobs, particularly middle class parents who can afford to give their children more spending money. Teenagers social lives are also very different these days - they spend a lot more time online which is essentially free if they have a phone, whereas earlier generations had to go out to meet up with their friends, which inevitably lead to needing money for bus fares, shopping or food. When teens do go out these days, the lack of free teen activities generally means they end up doing paid activities which their parents will give them money for. There is less incentive for teens to need to work.
3) Jobs for teens are few and far between. Both DH and I had part time jobs from the age of 13 - DH had a paper-round, I had a job washing up on a Sunday afternoon in a pub where my dad did shifts. Most of my friends also had part time jobs from 14-15.
Paper rounds are virtually non-existent these days and no-one will take on young people who are under the age of 16 because of insurance reasons - eldest DD couldn't even get a voluntary position at a cat rescue until she was 16 and there are a lot fewer shops, pubs and restaurants around than there were 20 or 30 years ago, which means less opportunities for part time work for teenagers.
Although we would have preferred eldest DD to find a job earlier (she is a September baby), we allowed her to wait until she'd finished year 11 due to her school anxiety (thanks to ND and OCD exacerbated by Covid and a generally shite school experience), but she was lucky enough to already have a job lined up where she does a hobby and it has done both her mental health and her confidence the world of good.
She has just finished college and while she doesn't know 100% what she wants to do career wise, she knows that she doesn't want to go onto uni so is starting to look at jobs. She is already determined to keep her part time job even if she gets a full time job elsewhere, and while looking for a full time job, is going to try and find additional part time work.
Conversley, her college friends whose parents didn't push the expectation that they had to work, struggled to get part time jobs and will struggle to get into full time work with the current tough part time / first time job market. Young people like my DD will beat them to it as they have experience, not just qualifications.
4) The general lack of opportunity and positive future for young people on a more global / political scale.
What is there to give young people any optimism for the future and any desire to work their arses off beyond being able to afford the next new iPhone? When I was at school / uni 25 years ago, we thought we could change the world. We'd been born into the longest peacetime stretch on record, the mid-90's onwards had seen an increase in positivity, global warming hadn't yet become the crisis that it is today. We had cheap travel, the world wide web was relatively new and exciting, technology was developing at a pace which suggested an exciting future. The world was our oyster and we could achieve anything through hard work and determination.
Today, we are on the brink of major world wide conflict, global warming is destroying the planet, it's harder for them to travel due to Brexit / cost / world wide instability, they are more likely to have to live with their parents until their mid-20's due to a lack of affordable housing and increasing house prices, those that go to uni are burdened with ever increasing debt, if they do meet someone and want to start a family, child care costs will cripple them for years.
Can we really blame them for having poor mental health or not being bothered to work their arses off for what they may perceive as very little reward?