To be fair, I think everyone underestimates the difficulty—including managers, the people that hire them, and the people who org companies to "require" a large number of people with these scarce skills.

While I agree ICs underestimate the difficulty, I think what ICs are usually responding to is that the managing isn't good. Whether that's because managing is difficult or because their manager is bad is in some sense not what matters. Those problem are the managers' job or the managers' managers' job.