They are rewarded for cutting the budget, and undercutting domestic workers. Until that changes, this problem will continue. Or workers could unionize.

As with many systemic issues in the U.S., it boils down to "publicly traded company must have highest profit possible so line on chart goes up". As much as I dislike FAANG companies in general for all their anti-worker efforts, I can't honestly blame them for making decisions that look good on the balance sheet. If I am a company, and I can choose to hire 10 U.S. engineers for $200k a pop, or 10 H-1B engineers for $100k a pop, I'm going to pick the H-1B engineers. Every H-1B or green card engineer I've worked with in-office has been extremely skilled, so I wouldn't even feel like I was "getting what I paid for" hiring them over U.S. citizens.