H1-B visa is their classification.
Companies wishing to recruit from overseas have several hurdles to go through. For each Visa
APPLIED for, the company filing the application has to put up 2,500$ - 3,000$. This before you are even sure you have a candidate.
Once in the US, same labor laws apply (almost). Salary shouldn't be much different than that of natives. Sometimes, though not usually, a company will dock pay to recover the cost of flying and initial housing. Most companies just eat the cost, and hope the recruit stays.
Also, the ability to screen technical skills is somewhat limited. You pretty much have to go on academic records (which could be fraudulent), and phone interviews.
Overall, only about 70% of the applications find recruits. That means 3 out of 10 times, companies pay the 2.5K - 3K and get nothing for it.
It's kind of like gambling
The alternative, which is very unpopular to native IT workers, is to outsource to other countries. I have yet to see this work the way it was planned, but that still doesn't stop the bean counters from insisting on it to save money.