I would argue that STEM subjects are the true places where people learn critical thinking - because those are the courses where students need to think hard enough to understand why some beliefs and claims are WRONG.

Whereas, in the humanities, students are often taught that there are no wrong answers, and are taught to value self expression more so than truth, or to disregard the idea of truth or logic at all.

But if you're not in search of truth or logical consistency, then there is no reason to think critically - and that is why people don't learn to do it.

The one thing that is not usually taught in STEM, though, that should be included in EVERY student's education, is logical fallacies. We need more people to be able to pass an LSAT. I wouldn't really lump that in with the humanities and social sciences in general though.