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.
You mudt have gotten lucky with your coworkers. Ive worked with people who claimed to be “experts” in a domain that didnt have basic skills. I would say 5% were excellent, 5% good. 90% worthless. Coupled with weird insular cultural dynamics, poor english and communication skills, poor throw it over the wall mentality. Its overalll a huge net negative for a company. Perhaps its different in FAANG. But in enterprise companies its very bad.