Here's an article with more details about the study: https://www.apmresearchlab.org/10x-adult-literacy#:~:text=by%20EMILY%20SCHMIDT%20%7C%20March%2016%2C%202022&text=This%20means%20more%20than%20half,of%20a%20sixth%2Dgrade%20level.

Dr. Iris Feinberg, associate director of the Adult Literacy Research Center at Georgia State University, points to under-served communities with "print deserts," poorly funded schools, and little internet access as being the places where the people with poor reading skills live. She also called it an inter-generational cycle of low literacy, so it's not just a recent problem with people not wanting to read.