I'm not being critical with your post and agree with a lot of it but I think you underestimate how disempowered some people are and how narrowly their opportunities have appeared.
So taking myself as an example: my school was very traditional (I'm quite old) and the careers 'advice' was just all about traditional jobs: fine if you want to be a lawyer, accountant, teacher, doctor or nurse but crap if you don't. Both my parents did boring office jobs (their assessment, not mine) and encouraged me to be a civil servant, work in the council or become an air steward (so they could get cheap holidays). None of these jobs remotely suited my personality or interests but no-one ever stopped to consider what I might enjoy. Not only that but they all put quite a lot of pressure on me to do one of these trad jobs.
If you've never been encouraged to pursue your dreams it can be quite difficult to imagine finding a job you enjoy. I was also brought up to be very compliant and that made it difficult to break out of the expectations.
I didn't know any actors, directors, editors, musicians, personal trainers, psychologists, sports physios, self employed people, speech therapists, cafe owners, osteopaths, website designers, architects, podiatrists, journalists, gardeners etc, etc so it was hard to imagine breaking out of the mould. I know there are a lot of people who do but there are I'm guessing an awful lot of people with less confidence and drive who find it harder without external encouragement.
I tried going to a careers counsellor and an employment agency who both offered traditional jobs and neither helped me to work out what I was suited to (I'm not saying they should, but just that it's not easy to find the right kind of support).
When anyone is unsure about what they want to do and asks for my advice I start with their values, interests and temperament. For instance, no point in someone who hates hierarchy, structure and deadlines going for a corporate role. No point in someone who hates self-determination and uncertainty being self-employed etc. If you prefer being outside, what jobs facilitate that. If you are creative, are there roles that suit that etc.