- China has great opportunities for riches
- Getting a US VISA is hard and painful when you come from a populous country like China or India
- My China-born colleagues seem to in general be more conservative, and Silicon Valley has become violently intolerant of anyone that holds an opinion different than the predominant view
Only the first reason is somewhat objective, while the two others cause stress in their daily life as their ability to provide can at any time be removed due to what is perceived as arbitrary reasons. Everything being equal, many of them have told me they would prefer the less crowded Silicon Valley.
Getting a green card is harder if you were born in China or India, not getting a visa, but once you've been on an H-1B for a sufficiently long period of time, you can only keep that status with a pending green card application. Switching employers at this stage is more difficult.
The DHS has said that they want to propose the end of the H-4 visa giving work authorization for spouses of H-1B holders.