I'll offer a counter-argument that teaching non-technical skills is at least as hard as teaching basic development skills. You just generally get more years of "free passes" to develop non-technical skills (ex., negotiation, conflict resolution, self-management, etc.) on the job than you do if you're expected to be productive doing technical work.

I've taught non-developers to produce, or at least understand, basic code typically in a few weeks while they were working on other stuff as well, but teaching developers to be good managers has always been much more difficult in comparison. I think it's easy to assume that since a lot of people aren't interested in writing code, it's fundamentally difficult to learn.