Allegedly literacy is above 90% but in reality you're looking at more like 50%. The lower half isn't literate enough to read newspapers or to reliably read signs. E.g. given a webpage with a [contact] link, they can't find contact information.
Never mind literacy, their fluency is debatable. They don't know what words mean. They sound like they're speaking but it's Pavlovian call-and-response; incapable of dealing with novel situations or anything even slightly unfamiliar or foreign. They aspire to being able to make it up as they go along. They know certain words are associated with certain situations but blank on why that might be. They can't articulate their thoughts, and indeed it's bold of you to assume they themselves have any idea what they're thinking.
As you may have noticed, the idea of being unable to fill out a 500-word essay is thoroughly foreign to me. Well puzzling, until I realized it's all Pavlov for them. Without a prompt they have nothing to write, and struggle mightily to prompt themselves. If the original prompt doesn't have a cached 500-word response, all they can do is spew meaningless garbage.
This may also relate to loneliness. If your verbal skills are dominated by Pavlov, then you can't think when you're alone. Or rather all you can do is review the Pavlovian response to silence over and over again. Oof. Need someone else there to cycle each other's state machine.
This may also relate to [creature of habit]. If your verbal skills are dominated by Pavlov, then you can't strategize. Even if someone straight tells you what to do, then you can't actually do it because you don't know what the words mean. This also applies to you telling yourself what to do. Attempting to think is a pure waste of time. Have to be whipped, and then try stuff at random until you stop getting whipped.