Why would they stay? China is seeing a huge boom in the tech industry and it's only the beginning. The future is there, not in SV. I'm kinda jealous of my friends who learned Chinese in college and are now working there.
Eh, if you think there is a bamboo ceiling in SV, there is a corresponding foreigner ceiling that is much lower in china. Most of us who worked in china shuffle out after 2 or 3 years, long timers beyond 5 years are rare.