I think we are talking about two different trends that have similar symptoms. I do agree there has been a noticeable anti-intellectual trend for a long time, especially in the West. (See also: Grade Inflation.) But that is separate from the drop in attention spans, which is relatively recent has been pretty strongly linked to digital stimulation, constant multi-tasking, and now short-form social media.

LLMs are an entirely new dynamic with significant cognitive implications, but I fear it will be hard to discern their impact from the falling attention spans and other long-term trends that have led to things like grade inflation.