STEM are also, I think, the wrong field(s) in which to rely on critical thinking to, _broadly speaking_, be taught. The technical background - programming languages or maths or basic biology / chemistry - that have to be assimilated before reaching that point are too high a hurdle for most students. Humanities, with a natural-language corpus + common experience, are a more-accessible approach. (The trivium, if you're familiar with classical-education terminology.)

That's not to say STEM courses can't teach critical thinking - they can, and must - nor that educators in Humanities haven't done a piss-poor job of it over the last half-century or so. That is to say that the general decline in critical thinking skills is mostly attributed to the decline in the status of and standards within the Humanities disciplines.