In the modern US economy there is a lot of talent that is in H-1B or other visa status in America. When a successful business places an ad for a new opening, almost every time, there will be at least one or two candidates who is in the US but either without employment authorization or under certain limitations. In the IT industry this number is way higher. Approximately 80-90% of applicants that reply to job advertisements in the Information Technology sector are immigrants.
In order to compete in the changing business circumstances, employers can no longer afford disqualifying such applicants right away. There are a lot of great applicants who are qualified and over qualified. But, most importantly, such applicants may consider lower salaries.