More because Europe had just spent half a decade murdering each other on a massive scale, and there wasn't much energy left for basic research for a little while after experiencing a couple dozen megadeaths and the various urban remodeling programs that accompanied them.

I'm not sure why you're being downvoted, you're right. We were large enough that we could find the talent, and the country was free enough so that private industry could drive innovation. Low taxes let companies reinvest. We know this is what happened because the success of free markets isn't a mystery, it's well studied and documented.