In other words, this isn't a real job listing. If the employer wasn't sponsoring the intending immigrant for a green card, it wouldn't exist in the first place.

In other words, this isn't a real job listing. If the employer wasn't sponsoring the intending immigrant for a green card, it wouldn't exist in the first place. The employer already intends to hire the immigrant. In fact, the immigrant may already be working for them on an H1-B or other visa. So it's effectively a job listing that is already filled.