Hasn't this always been an intelligence thing? I think across all societies and eras we find that generally a a rather alarmingly large section of population is unable to grasp basic written instructions - and that section usually increases to the majority of people, when we start getting into things like an employment contract, or mortgage document.

In an international comparisons, USA comes out somewhere in the middled of developed countries - as it always did. And the differences between countries are not that large.

54% of adults have a literacy below a 6th-grade level is simply not a some kind of catastrophe and it does not mean those people cant read. There is this idea that 6th-grade level is almost like not knowing how to read, but that is simply not the case at all.