Many developers are medium sized fish in small ponds, where they can get away with moderate effectiveness, bad programming habits and little study, or, if they are good, they easily stand out and enjoy the honor of getting the harder tickets assigned, yet may not ever be really challenged.
These top paying companies all seem to do quite complicated stuff, serve a lot of users reliably and implement major features quickly. FAANG codebases seem large and involve a lot of (custom) tooling that devs need to grok and processes they need to understand. Just the author's passing advice to study up for those interviews means ... many hours of study in that "100%-concentration-mode" that many people are not willing or able to put in even for 1 hour.
No doubt there are some cosy pockets in FAANG but, ultimately, building AWS or Azure from nothing can simply only be done by a certain type of person who is willing to bring a certain amount of effort. And those people the market rightfully grants the appropriate salaries. Right?