edit: the parent has since edited out the flamebait.
Maybe, or maybe when silicon valley was busy growing exponentially Europe was still picking itself up from the mess of ww2.
Trying to blame a single reason is futile, naive and childish.
The US was out-innovating Europe a long time before WW2, we had faster, more extensive rail systems, superior high rise construction, earlier to electrification, invention of the telephone, modern manufacturing (Model T), invention of the airplane, the birth of Hollywood and modern motion pictures, the list goes on.
I think it's funny how the US, Canada, and Scotland/the UK all simultaneously claim to be the home of the telephone.