Meaningful work is not about fulfilling someone's dreams or them "becoming entrenched in the doing of it".
It's about the work itself having meaning.
If farmer Joe didn't farm, people wouldn't be able to eat their veggies.
If some office drone doesn't do his job, chances are nothing much would change to the output of their company (assuming the company is actually doing something meaningful and not harmful itself). If anything, some jobs just create more work for other parts of the company, without meaning (e.g. just to satisfy some state or company bureaucratic procedures) as opposed to improving workflows.
>ut how common is it for Newboy Johnny to boisterously look upon the world with his newly minted College University degree in hand and say "Yes, this one lifetime career path is just for me and I'll take it!"? It's not 1952 any more. I don't know why anybody younger than I am still believes that any of this is real.
They might not believe that any of this is real today, but they could very well believe that the old way is better, and that as active citizens that shape our society and steer it (as opposed to mere pawns that go this or that way randomly as technology or time changes) we should recreate that kind of environment.
Changing multiple jobs throughout one's career should be a personal choice, not something imposed by a thankless and merciless corporate consensus -- alongside discarding people after a certain age because they can hire young starry eyed idiots to pay them way less while overworking them.