On top of what people have noted about No Child Left Behind and underfunded schools, I think some people are missing just how unnecessary it was to be able to read before the rise of the internet and smartphones. My dad is 52. He used to brag to me all the time that he could read and he passed high school. This was a valid thing to brag about because if you took an account of blue collar men in the area they couldn't. They didn't see the point because why would you need to read? Your wife who could read at a 6th grade level or above could read and it's women's work to handle to go to places and pay bills and all that BS. All the women in my family can read at a basic level because of gender roles. Now could they read well enough to be ready for college, well that's up for debate, but they're good enough for a text conversation. The men were a different story. I remember when I was a kid they had markings in the street so the bus drivers could know the routes. It wasn't assumed they could read street signs.
So just consider anyone gen X and older and consider that the older they are the more likely they are to either be illiterate, functionally illiterate, or just have a basic ability to read and nothing more. For the younger generations actually illiteracy is basically impossible, but functional illiteracy and only basic is highly probable due to high rates of poverty, underfunding in schools, and the high incentive schools have go pass kids at any cost.
