[mehaveaccount]

People don't pay for linear regressions. They pay for discrete things: what is my best option among my three clear courses of action. Linear regression can be a tiny piece of a larger argument in favor or against one option or the other, but that alone doesn't make money.

[Bootvis]

That's obvious but not at all what I responded to in my post.

I responded to the claim that ML courses start with the definition of precision and recall. In my admittedly limited experience those courses start with linear regression and mean squared errors. After that, there is so much generalization possible and that doesn't include precision/recall.

You make money by solving someone's problems, making money by stating definitions is only done on TV quizzes.