I wonder the same thing. Some sub-contractors have been caught using illegal workers even in areas that are supposed to be secure- like military facilities. There has to be a loophole of some sort that needs to be plugged.
I have an indemnity clause in my sub agreements stipulating they use e verify or comparable method and assume all liabilities and penalties for using illegal immigrant labor. I guess what I’m getting at is it seems to me a lot of illegal immigrants are starting either s corps or llcs. It seems to remove them from e verify issue at the prime contractor level. At some point I think the IRS comes after said corp or llc but that could take years.