Hotelling's law and Nash equilibrium can partially explain why so many "next silicon valleys" haven't panned out. It's also interesting that the valley is in a jurisdiction with such pro-employee laws.
I'd attribute the difficulty of creating the next SV partially to capital/talent concentration being a coordination game (https://en.wikipedia.org/wiki/Coordination_game) - for any individual small developer, entrepreneur or investor, it makes sense to go where they have the best chances to thrive.