I doubt the engineers who designed it (and who are supposed to inspect it) are illegals.
No one suggested that, just you.
Corrupt greedy contractors hire illegals to do the actual stoop labor to maximize their profits. This is no secret and in fact illegals completely took over the construction industry years ago. Even those drooling in cups know this. Those bankrolling these project winked and nodded as it maximize their profits..
Profits regardless of consequences...