Is it just about having dense industrial zones? I would have imagined cost of labor to be the major cause of price differences.

A lot of the cost of silicon valley labor comes down to extremely high housing prices. A lot has been made of how the tech boom was simply a wealth transfer from investors to bay area real estate + homeowners.

Sure but even if you exclude Silicon Valley, the minimum wage for a US worker must be a fair bit higher than the equivalent non-US worker.