Here's how it works. A company like Cognizant gets as many H1Bs as it can via an army of applicants and subsidiaries in India to game the lottery system. Meanwhile, companies in the US that want to pay less for IT functions create job descriptions that are tailored specifically to H1B applicants (if you've ever wondered why there are mandatory requirements for a very specific set of systems experience and education, this is often why), then post those jobs only where they are unlikely to be found and tell American applicants who do manage to find them that the position only pays [20% below real market rate]. Now you've got a US company that can legally say they just can't find any qualified domestic applicants, an H1B-focused staffing company that has tons of people it can bring in and rotate through regularly, and wages that are depressed. Net result: IT departments at large companies that are 40%+ staffed by H1B contractors.

I've seen this happen repeatedly at clients you've definitely heard of and it creates a situation where there are plenty of Americans who would work these jobs, but the salary/benefits being offered just aren't competitive.