A significant number, or possibly a majority of, adult native English speakers in the US actually speak English significantly below their formal education level: around 90% of them have at least graduated high school, but 54% of them read English below sixth grade level.

Standard English competency testing for the citizenship test is a joke (you have to read and write one of three sentences in a manner that demonstrates basic comprehension and familiarity with the language). But even so, there's a sizable number of native adult English speakers who would fail it.

So while they may have had to learn English in school or used it to pash their citizenship test, that's no guarantee that adults still speak it well enough. That's not particularly surprising, given that there are large, non-English speaking communities in the US. Someone who's passed their citizenship test in the 1980s and has spoken English maybe once a week afterwards in a shop or a restaurant is likely to have forgotten most of it.

inb4 "but you have to know it to come here": kind of (adjusting for the barebones testing), but the largest group of low-English literacy adults is actually white, native-born Americans, and most low-English literacy adults are native-born: https://nces.ed.gov/pubs2019/2019179/index.asp

do you expect this to be the sole example you've failed to consider?

In the end it is pure xenophobia. Pure, cruel xenophobia, putting people in harm's way because you couldn't care less about them.