US corporations bring many technical workers on H1B visas to the US on a pretense that there are no Americans who have the required skills. This is not always true – the salaries of H1B workers are lower than the salaries of Americans, and foreign workers on H1B visas cannot leave the corporation to look for better employment in the US. On average, a corporation saves between $10K to $30k/year by hiring a foreign worker. In the US, there are even companies which teach American corporations how NOT TO HIRE American workers, but hire foreigners:

 Here are examples:

https://www.youtube.com/watch?v=Gi1R4iDx3Lg​

https://www.youtube.com/watch?v=TCbFEgFajGU