I've been away from teaching for a year. I was teaching writing, so I didn't test for reading comprehension. I thought I gave them a reasonable amount of reading to do, considering the time required for the significant volume of writing that I and my colleagues assigned. We all felt it was important for them to read, too, because writers have to read. How else will you know if your ideas are original? And, of course, people who don't are at a huge disadvantage when it comes to the mechanics of writing. I never did figure out why people who didn't like to read even wanted to write.
I'd say that a significant portion of them were able to read the assignments just fine, and they included sophisticated texts--Hamlet, the Brontës, Frankenstein. Some of them surely skipped the reading and sat out the class discussions as best they could. I'm pretty sure I could tell who they were.
Toward the end, I observed some things that I thought were shocking. I had a graduate student tried to use AI to outline his novel, and the result didn't even resemble the assignment I'd given.
I also noticed that a number of students didn't seem to grasp how a novel is laid out on the page, because they were clueless about what I meant by "scene breaks" until I projected a published page on the screen and showed them the white space that breaks a fictional narrative when there's a change in POV character, time, or place. I finally realized it was because they were listening to audiobooks. I had to change my syllabus to specify that, although audiobooks are a completely legitimate way to consume text for other purposes, they needed to read printed books (paper or ebook were both fine) for my class. And, of course, I explained the reason for this change.
In short, written word is competing with a lot of other kinds of media these days. (Movies, TV, games, the internet--all the usual suspects.) Games, in particular, are a huge part of young people's lives these days. I privately thought that many of my students really wanted to write video games, but that wasn't what our program taught.