Silicon Valley is the home to most of the tech industry in the US. Pretty much every major tech company has an office there. Around the 1990s the immigration system started becoming more open towards high skilled immigrants which attracted a lot of rice and curries. Silicon valley is also where engineers get paid the most, so most of rice/curry immigrants went there.
The reason why there are so many wmaf couples in SF is because of the lack of young white women there. The average home price in SF is around $1.5 million and rent is very expensive too. Most jobs in SF are technology related and young white foids typically settle in a city like NYC or chicago or boston because they are more affordable and have jobs that arent demanding. Foids dont want to work in software jobs because they usually tend to be very intensive they also have to work with a lot of incels.
Because of the rarity of young white women in SF, a white woman who would be a 4/10 now has the smv of a 9/10. As a result the only option a white man has is to marry outside of his race unless he is chad ofc.