The dirty secret is that there's a whole class of jobs, mostly decently paying white collar jobs, that have most of the training on the job.

Hell most of the jobs that only require an undergraduate degree involve extensive on the job training; college is used as a weak signal for aptitude, interest, and class not really capability (this is the entire business model around coding boot-camps).

I got about 3 days of on-the-job training, pitched at showing generally skilled programmers the company's specific tools, practices, and environment. The rest was just being thrown into the normal day-to-day work, with the expectation that I'd ask more questions and make slower progress at first.

You can't just throw a laid-off factory worker into that position, though I agree, you can probable prepare him to handle it more efficiently than a 4-year BS degree program, which is what bootcamps are looking to capitalize on.

It matters a great deal to the employee to have been put in a situation like that before (homework & hobby projects) and developed a decent intuition & familiarity. It matters a great deal to the employer to know that that the candidate has done something like this before and will be substantially likely to succeed. There's a little more going on here than class signaling.