Though teaching did not become my main career, I've taught at all levels from kindergarten to university, at both traditional classroom and experiential venues, in a variety of subjects (though mainly science-related). I also was a college student in a variety of forms for four different decades. I have witnessed the degradation of logic and critical thinking, often to my great advantage when I became an older student, and have studied causes to this effect.
I note in particular three causes, yet let's begin first with what is not a cause. "Kids these days" does not apply. Natural evolution does not work that fast. Humans are hard-wired to learn new things; we delight in it in fact, whether it happens to be how a car engine or video game works instead of school subjects. We would not have survived without this hard wiring. The fault, then, lies in factors beyond the student.
Every study I know contrasting the effects of different conditions on learning breaks down when parental support and/or involvement is controlled. Private school or public? With the same parental support the differences in success are minimal. Rich or poor? Same result. Proud parents of successful students is generally a self-fulfilling condition. The pride they take in their children's education leads to superior results. Over the past five decades there has been declining parental involvement in children's educational success. The reasons are not worth discussing at this point and could land this thread in the cesspool.
This impacts both spelling and critical thinking, but there are additional factors that impact critical thinking further. The biggest reason I am glad teaching did not become my main career is how the curriculum has been geared ever more towards teaching to the test. The test could be quite "advanced," one could rote learn the theory of relativity, yet this does little for training students towards critical thinking.
The third reason is that, as a society, we have gravitated ever more towards what I call a "marketing culture." We market stuff; we market policies; we market beliefs. Marketing appeals to a different part of us, a part ruled by emotions more than critical thinking. Over the past few decades every aspect of our society has become more emotional and less empirical, including our schools.