I don’t have data on this, but I’d guess the top tier VCs attract and have deal access to top tier startups, which are more likely to perform well. Then, when those perform well, the next top tier startups will come to them again.
Perhaps someone else would be able to confirm my assumption on this positive reinforcement loop.
Also, these days you can get a reasonably good comp and still be at a startup. Sure, it will not be as much as FAANG, but it’s still good, and you get to work on an environment that’s more stimulating and allows you to try things out.