Its people who've been stratified out of the workforce, and can't pay insane rates for education of either university level or trades.
How exactly are we tracking this? I know in the USA, we cheer and hooray when the unemployment numbers go down, but those are pegged to "how many people get unemployment"... And after at most 2 years, they drop off. And that makes the numbers on 'unemployment' go down!
Well, yes and no. It’s true that university is expensive (but you don’t need to repay loans until you are earning over a certain threshold). However it’s also true that if you take an apprenticeship a) you will be paid during training and b) a skilled tradesman or tradeswoman can easily out-earn most graduates, and this is well known.
if you can find and be accepted by one
In my area, we have a few trade unions and a steamfitters training facility. They take new potential apprentices 2x a year. When I looked into one a while back, there were over 500 people in front of me on the _reserve_ list. I nope'd out and looked for other avenues. There were a few others, but also had similar insane lines with estimates of years before getting an apprenticeship.
So yeah, while that path does exist and costs no cash out of my pocket, its mostly wishful thinking that this is a "get in, learn and do, and get paid" and more of a "hurry up and wait... maybe".