Foreign workers are cheaper because you can use their visa to extort them. If they get whiny about pay, you threaten to fire and deport them.

It's really that simple. SV likes foreign workers BECAUSE SV salaries are high. Businesses will do literally anything to save a few cents, at any cost.

There are enough qualified domestic candidates. Your bosses don't want them because domestic workers demand wages that fit domestic cost of living. Foreign workers can be extorted into accepting much less than a domestic worker will.

This is all very simple and straightforward. Your big mistake here is in assuming that capitalism is fundamentally moral or logical. It is not. Literally only one thing matters and it's maximizing profit at any cost.