Because even the mythos of Silicon Valley's origins is incorrect, and this has led all the attempts to copy it to be similarly wrongheaded.
For example,
every single answer on this page about Silicon Valley's origins is missing key details.Most stories about the origins of the Valley (including Paul Graham's "How to Be Silicon Valley" - see
http://www.paulgraham.com/silico... and
http://steveblank.com/2009/08/17...) totally misrepresent the Valley's history in typical Northern California hippie fashion, citing a techno-utopian origin myth of plucky entrepreneurship, daring angel investors, and smart engineering students out of Stanford - all arising organically without central coordination.
In fact, Steve Blank's, series of pieces on The Secret History of Silicon Valley (see
http://steveblank.com/2009/04/20...) shows that what jumpstarted Silicon Valley was actually
massive and sustained top-down investment by the military industrial complex.
Certainly, Stanford University was involved, but as the nexus of research led by Fred Terman, who directed a staff of over 800 people to build Allied military technology during WWII. Afterwards, as the dean of engineering at Stanford, he helped to create Stanford Industrial Park, where a large number of high-tech firms, many of them comprising the military-industrial complex (e.g. Varian Associates, General Electric, and Lockheed Martin) based their operations. In fact, according to
http://steveblank.com/2010/03/08..., by the 1960s, the Lockheed Missiles Division in Sunnyvale (you know that huge complex next to Hwy 237 with the enormous radar dishes?) was
the largest employer in the area - they came to the area in 1956 and grew from 0 to 20,000 engineers in four years.
That's how the enormous concentration of technical minds came to be in the region: it wasn't just a school and some little startups and angel investors. Large-scale, sustained defense spending fed huge technical industries that hired enormous numbers of engineers from across the country, who moved their families into the region.
So the real answer to any country or state (ha) that wants to copy Silicon Valley is this: pour billions of dollars into a tightly-clustered region filled with military contractors and make it their mission to develop advanced military technology for a decade, which will prompt all the smart technical minds to move into the area, creating the necessary technical population to jumpstart an "innovation" region. Unfortunately, very few countries spend the requisite proportions of their budget on military research the way the United States did in the 1950s and 1960s, so this is basically impossible to replicate - except for perhaps China (kind of), which is the only country having some measure of success with creating a startup economy.