I'm not sure how exactly it works but if I had to guess, the non-local talent would have fudged resumes showing they had the relevant experience. It's not like the relevant Labour departments would actually do the background check on hired candidates. All the companies/consultancies need to do is to show that they couldn't find a relevant candidate locally to satisfy the sponsorship requirements.
Note that I'm not just talking about US. Most countries in Europe have the Labour Market tests requirement before a foreigner can be sponsored for the position.