From the https://nces.ed.gov/datapoints/2019179.asp link - "U.S.-born adults make up two-thirds of adults with low levels of English literacy skills in the United States."

I don't think its any more likely for an illiterate person to pass through the immigration system than it is for same person to get AWS certification.

It's most likely a factor. It's also not too obvious whether those numbers are high compared to any other country, because it's one of those things that every country has its' own unique standards and methodology for measuring. For instance you might think that North Korea is the gold standard of literacy, at 100%, or you might think that they likely have some serious issues with the methodology they use for measuring that.