[calebkaiser]

Anecdotally, as part of my job, I've taught ML concepts to a lot of people. I don't know if I've ever worked with anyone who was simply too "unintelligent" to grasp things. The bottleneck, as for most things in my experience, is time and motivation. In any niche of ML, there's just a lot of things to learn, particularly if you aren't starting with a particularly math-y background.

[hilux]

You were probably working at a fairly advanced tech company. As were the people you were teaching.

If by "ML concepts" you mean "how to implement ML" - do you really think that people who got to a job that required learning this, represent the population IQ distribution?