Being south asian myself - I suspect that the high achieving immigrant-and-immigrant-descended populations gravitate towards technical fields and Ivy leagues for different reasons than American whites do. Coming from hardship and generally being less WEIRD, they psychologically share more in common with the middle class and even blue collar workers than the Ivy League upper class - they see it as a path to success rather than some sort of grand purposeful undertaking. (One of the Asian Professional community I participated in articulated this and other differences in attitude as a reason that Asians often find themselves getting passed over for higher level management positions, as something to be overcome).

Lesswrong tends to appeal to abstract, starry-eyed types. I hate to use the word "privilege", but there is some hard to quantify things, like degree of time talking about lesswrong-y key words like "free will" or "utilitarianism", which are going to influence the numbers here. (Not that asians don't like chatting about philosophy, but they certainly have less time for it and also they tend to focus on somewhat different topics during philosophical discussions and use different words. They've got a somewhat separate religious-philosophical tradition)

Another possibility that might make an even bigger difference is that, lacking an organized religion to revolt against, Asians may less often be militant atheists and skeptics. Lesswrong and Overcoming Bias owe part of their heritage to the skeptic blogosphere.

/speculation