A lot of people did leave when they had the chance.
It surprised me how many people stayed. As another poster here noted, a lot of very senior people stayed who were at or near the VP level stayed. Some of them wouldn't know what to do with themselves if they left. And I think some like the status and power that comes with managing a huge org.
But I was also surprised how many individual contributors who became rich stayed, and just continued to write software or Verilog or whatever. They were bright people, and nobody messed with them because they were well-known and were just allowed to do their own thing.
Watching what people did when they came into a lot of money was an interesting life experience. Hell, watching what I myself did when I came into a lot of money was also an interesting life experience.
When I first came to Silicon Valley I was so excited to be surrounded by so much great technology. I got to play with so much very expensive test equipment: it was like being a kid again. As time went on, it wore me down, and it wasn't so interesting. I encountered a lot of bad actors: the other anecdotes in this HN post sound very familiar. When I had FY money, I left. At that time, I hated my job. I have no interest in writing code or using fancy oscilloscopes and logic analyzers. I don't want to look at another C function as long as I live. And I will never go back to Silicon Valley.