In economics, Google, Microsoft, Intel, Facebook, Apple have what are called "monopolist rents" a form of "economic rent" which mean because of the nature of their product they get higher profits than they would in an efficient market.
A result is that the leadership of these firms are worth tens of billions of dollars in the case of Google (two leaders), Microsoft, Facebook). Instead of sharing the benefit of the "monopolistic rents" the leadership hire H1-B visas and also colluded with each other to keep tech labor rates low.
Differences in salary are negligible? Well, then let's give a 10% raise to all engineers employed by Google, would that work?
It's not just about paying H1Bs less than American workers, it's about keeping salaries low for these very workers as well.