Plenty of people will learn only that which they perceive to be required and no more. People managers don’t seem to be an outlier here.
It isn't just the managers doing this. Anyone who isn't in a position of authority but has knowledge of the state-of-the-art, research on it, etc. can tell when someone in that position is pushing their ideals over actually having done research or doing logic beyond a bunch of unquantifiable 'what if' arguments. It takes 5 minutes of online research to dismantle their arguments. But it still happens regardless, even in CS and SD where myths are pushed as absolute truths.
"My team always give 110%" is better than "I treat my people like adults with lives of their own", even if it gets much poorer results.
My favorite myth is the one that I hear surprisingly often, from educated and intelligent people. I hear it, because I ask them why they bias for only young people; even in senior management, architectural, and mentoring roles.
They explain that young folks can do the impossible, because they haven't been told that it's impossible. It's a really compelling myth, reinforced by founders of successful unicorns, sharing it as their "secret sauce," as opposed to obsessive work, intelligence, and an enormous dollop of good luck and timing.
I call it the "Don't Look Down" Fallacy.
When Wile E. Coyote runs off the edge of a cliff, he stays up, until he looks down.
If you don't allow anyone into the team that yells "Look down!", then you can fly.
Absolutely. I didn't mention people that tell you to stay away from the edge.
In many cases, timidity (often a reaction to past trauma) can be debilitating.
I remember when I was interviewing at startups, and Every. Single. One. -Every one, described themselves as "unicorns."
The harsh reality is that, for every unicorn, prancing around the tech industry, there's a charnel pit, filled with the corpses of 10,000 goats and jackasses, with horns glued to their foreheads.
Not all timidity is bad, and, sometimes, ignoring warnings can be quite fatal.
I’d probably still agree with your statement though. They also definitely don’t teach us how to manage.
For that reason, training for public defender managers is usually legal training and subject-matter-specific leadership training. For example, we get a lot of training time on how to support lawyers through burnout. It is almost unheard of that we would get training on abstract or generalist management practices. Executives see it as off-mission and managers think it's a waste of time.
This problem is exacerbated by being a correct strategy at a certain (small) organizational scale, but the paradigm falls out of alignment as the organization grows. It's hard to build an intentional culture of management in an already-existing organization.