Like most of hacker news, I think you vastly underestimate really how replaceable smart and skilled people really are. There are literally millions of them, most with far lower pay and conditions than offered by FANGS.
You are forgetting how expensive it is to replace smart and skilled people.
There sure are millions of them, sure, but not necessarily millions of them available when you post your opening. I know because I am searching for senior Java devs for a stable, global, wealthy corporation and yet it takes months to fill positions.
Then to the expense of searching you need to add the expense of the guy having to spend at least a year on the job to really become productive, learn the system, the organization, learn the problem to be able to effectively design quality solutions, etc.
If this guy leaves in 2 years on average you have spent most of the time basically searching for him and waiting for him to warm up.
Smart and skilled people spend a bunch of time learning your problems, figuring out solutions, only to take all that knowledge and experience with them to be replaced for a green guy who will have to start mostly from scratch.
Even more, as it is measured, the more replaceable you render yourself in your work the smarter and skillful you are, and the quality of the work is considered higher.
