I'm all for trade schools, but I feel like that's a slightly orthogonal issue.
There's no immediate reason to expect a company to help train up employees (not just juniors, but moving people from every level to the next step)....unless those companies want to improve the outcomes of their staff, want to improve morale, and want to resolve their perpetual difficulty in finding people senior enough for their needs.
Don't do it out of social responsibility, do it for keeping your business functioning long-term. I've worked too many places that have almost exclusively senior devs with more work than they can handle. They focus on hiring MORE senior devs (but don't have much success), meanwhile their senior devs are spending a lot of time doing work that junior devs could accomplish.
There are numerous side-effects too - mentoring (if you like it) can help improve your own skills and outlook. Fresh perspectives are always good, and once someone gets their first few years in, they will occasionally have insights that seniors can learn from. At the best places I've worked the more senior devs have wider perspectives and deeper experience, but the "who is right" between junior and senior becomes more of a statistical model than a certainty.