The reason is fairly simple. America has a workforce of roughly 120 million people. A fraction of those are white collar workers. A fraction of those are softwa

The reason is fairly simple. America has a workforce of roughly 120 million people. A fraction of those are white collar workers. A fraction of those are software engineers. A fraction of those are willing to live in coastal cities. But America has the 5 largest tech companies in the world, and significant presence of foreign companies with development centers. These companies hire millions of workers every year and would prefer to maintain most of their workers near their HQs. Thus they need a huge supply of foreign talent to complement their American workforce. After all the world has 7 billion people. If let's say visas were extremely difficult to acquire, these companies would open massive development operations where it is easier to hire global talent