On the one hand, you have people for whom “Dick and Jane have a dog” is too much. They can’t decipher it and read it. There are a lot of people like this.
On the other hand, you have people who are fairly literate but who cannot manage the stamina to read a one page essay. It’s too boring. They lack the attention span. These people also “can’t read” and there are a lot of them too.
I agree with your population breakdown, but I would suggest that the latter portion of people would fall into the category of "won't read".