"Silicon Alley" (New York), "silicon roundabout" (London), and so on are simply natural, technologically focused extensions of the existing economies in those areas.
If you want to create a Silicon Valley in Europe, it will take decades until it can compare to Northern California.
Now that you put it into a sentence, I find it less surprising that Switzerland is starting to brand itself as "Europe's Silicon Valley".
And then there is taxation, mentality, fragmented language environment and so on. I don't see it happening.
VC presence in Israel is probably second only to SV and the rate of startups per capita by far exceeds any other country.
What Israel loses to SV is primarily cultural; no one gets the US consumer better than SV, that's why Israel is more focused on enterprise, security, semiconductor etc.
https://en.wikipedia.org/wiki/Sophia_Antipolis
Btw, the reason why they failed is a banking system that hates bankruptcies. If your startup fails, you won't get any credit (yup, better get a mortgage before starting a company) for at least 10 years (I think it was 20, but am too tired to search for references now).
China is a serious contender to SV.
Europe doesn't have a Silicon Valley because every nation would want it to be in their backyard. But even if the concentration isn't there and the number of exits > $1B isn't as large (or the number of $1B and up companies isn't as large) we have plenty of solid performers.
It's not going anywhere geography-wise.