I don’t really believe these reasons or at least they don’t match what i’ve seen. I can only speak for FAANG: I think this is more compensation based than anything else.
In an effort to level the playing field FAANGS establish levels. Levels have salary ranges. Salary ranges mean top performers, the people who drive the culture of the entire org, can only be paid some amount more than bottom performers. By keeping these bands too tight the top performers can get better pay elsewhere and leave.
When your first top performers are leaving each one hits hard. Once it’s regular the culture becomes different, this isn’t a place to stay and grow, it’s a place to be a launchpad for the next place. And without top pay you won’t attract top talent so when these great people leave you replace them with average people. This reinforces the beliefs.
The other side of pay is current valuations are insane. Many startups are getting A, B and even D rounds with 300-500x (i’ve seen higher than 1000x) revenue to value ratios. Your FAANG may hope to 2x or 3x in stock value while these startups promise 20-30x returns. So you have to pay even more to beat the potential earnings they could get at a startup.
My theory is not that all pay has to change to keep people, but as a FAANG you need to spend to keep and attract the best or you risk losing everyone. When you work somewhere and all the best people want to stay, or when you work somewhere and more good people join; it’s really hard to mess up that culture