Not all STEM is the same. Some of it, including medicine, includes massive amounts of memorization, in addition to analytical application of that information. Most engineering, on the other hand, doesn't ask you to memorize shit, it's all analytical application.
One thing in common, though, most STEM reading is dense, hyper-factual stuff, nothing that asks you to accept or reject or criticize it. It's pretty much 100% "this is it." You rarely if ever compare and contrast histories, authors, philosophies, politics or policy. Except in your 12 hours of electives, which most STEM people do well on.
So, you're still thinking, and actually in a way that's quite analogous to critical thinking. But you aren't "practicing" it, so to speak, on subjective subject matter.
And, I think whoever posted about taking mental shortcuts on non-essential (ie non-work-related) information, e.g. news, is spot on. Probably a habit that develops during school.