From the cited article:
But middle- and high-school kids appear to be encountering fewer and fewer books in the classroom as well. For more than two decades, new educational initiatives such as No Child Left Behind and Common Core emphasized informational texts and standardized tests. Teachers at many schools shifted from books to short informational passages, followed by questions about the authors main ideamimicking the format of standardized reading-comprehension tests. Antero Garcia, a Stanford education professor, is completing his term as vice president of the National Council of Teachers of English and previously taught at a public school in Los Angeles. He told me that the new guidelines were intended to help students make clear arguments and synthesize texts. But in doing so, weve sacrificed young peoples ability to grapple with long-form texts in general.
If they are reading a novel, and say there is a description of a dinner party. If, in their previous schooling, they would be tested on the details of the party: how many people attended, what color dress did Susie wear, etc, and then they try to read a novel thinking they have to recollect all these details, I can understand how they would feel overwhelmed.