When I went through school, reading comprehension involved reading a few full pages, followed by questions to test understanding. Nowadays, reading comprehension involves a 25-50 word passage (about the length of a tweet). It's just plain easier.
When I went through school, entire books were assigned for reading, followed by book reports and tests on retention of the entire book. At least a solid dozen books would be read over the year, in addition to several plays, a poetry unit, and some short stories for good measure. I'm watching my kid go through HS english. The books are really good, but they read way less overall, and each book is broken up into many several-page sections that they're tested on in sequence. It's much less demanding. At no point does my kid say "aw man I gotta read 50 pages of my book for english". That was pretty regular in my time, at least in the honors course.
The article seems focused on reading and writing. Yeah, I'm sorry to say that emphasis on rigorous reading and writing has degraded over the past 20 years. People who train to bench press 100 lbs regularly are gonna be stronger than people who train on 10-15 lbs. Is anyone surprised?
I'm not sure this applies to math and science. STEM in the US seems to still be fairly solid.