I guess the reason I feel it's different than "stupidity" is I think of that as a trait, whereas this thing feels like a new (or at least increasing) behavior.

Not like "you cannot derive basic conclusions from simple inputs because you were unfortunately born without ability to do that", but more like "you refuse to derive basic conclusions from simple inputs because _________________."

The reasons aren't clear and are possibly complex and subconscious, but it seems more about refusing to do the basic mental processing, despite having the capability to do it.