Why do we not introduce the concepts and professions of "Academia" to younger students?
In terms of work:

Because the world is gigantic and varied and for all its intriguing features, academia is only a small part of it.

Think about your high school cohort and where they ended up. Some of them are seeking a baccalaureate degree. Many aren't. Some of the latter group are in trades, others working retail or food-service, others health or other personal service, others finance, and so on. The number that will even so much as consider a career in academia is tiny; the number that will actually achieve one even smaller. Why, then, privilege academic work?

In terms of information sources:

I do think it would be worthwhile for more high-school-age students to be taught a little epistemology ("how we know what we know") with specific reference to academic research. This happens to some extent with science fairs and National History Day and so on, but more would be welcome!

Again, though, academic research is only one information source among many... and given how much of it is paywalled away from everyone who isn't a career academic, what's the point of making a big deal out of it to people who mostly won't ever have access to it?