I think you are confusing “citizen” with “legal resident”. It’s illegal to hire someone (in the US) who is not legally able to reside there but there are many options (citizen, permanent resident, i94 visa, federally recognized tribes, refugee visa, and a bunch more)
You're right of course. I read "citizen" and interpreted "has the right to work".
I'm not a US citizen and I legally worked there for years. Visas are not an edge case.