Because both countires have shown they could move up the value chain.
For example, thailand, philippine, malaysia showed they can't move up stuck in mediocrity. Taiwan also not qute there because mostly its high tech manufacturing and little innovation and core technologies.
Actually Taiwan is doing pretty well. You open up all those high end game consoles, and the heart of those game consoles are Made in Taiwan graphics chips from nVidia and ATI. These are ethnically Chinese controlled companies with strong Taiwan connections with labs in both Taiwan, Canada and the US.
You will find that Taiwan has a strong hand with Silicon Valley companies, as these companies have strong ethnic Chinese and Taiwanese connections. These companies subcontract their chips to Taiwan free play fabs, and free play fabs like TSMC has no equal in the world in their abilities to manufacture very complex chips at low volumes and yet in low prices. Good examples are the graphics chips, or the motherboard chips, that's the heart of every PC. Why does the Taiwanese dominate them?
Memory chips, like those pursued by companies like Infineon, are inherently low tech in comparison, since a memory chip is essentially a matrix of capacitors. Comparing a memory chip to a motherboard chip would be in analog, comparing a large farm to a large factory. The complexity of a motherboard chipset is that this chipset literally defines and integrates all the functionality you know as a PC into a reality.
This ability to manufacture such complexity at low prices have spread out to lap tops, cell phones, PDAs and other computing devices. The actual implementation and design of the motherboards for the iPhone and iPods are done by a Taiwanese company, which then contracts the assembly in China. The Xbox 360 and the PS3 also have motherboards designed in Taiwan and subcontracted by Taiwanese companies to who knows where.
Taiwan is a small place, it simply does not have the resources of Japan which has a population many times bigger. S. Korea is at least twice the population of Taiwan. So Taiwan cannot be master of many industries, but it has to select which industry its going to be good at, then be good at it. And this has worked very well for Taiwan, and no place in the world is better at systems design and integration than the Taiwanese PC companies.