It's one of the two or three biggest reasons, and definitely not the sole reason. The modern system of industrial-scale venture capital available in the US - going back widely four plus decades - is rivaled only by China in the last decade. More broadly that culture of risk capital spans every tier, from the smallest angels to the biggest VC firms. The comprehensive nature of it is exceedingly rare among nations. It's also now a very old phenomenon in the US, going back to the earliest days of the industrial revolution (everyone from Tesla to Edison to Ford were financed by what was essentially venture capital).

Most of developed Europe, except for a few nations, scores well on having low corruption, comparable to or better than the US. Western Europe also widely has a strong social safety net that should be encouraging to entrepreneurs from a life-risk perspective (which may actually result in the exact opposite outcome: a culture of lower risk taking; the culture that will install the world's most elaborate social safety systems, is more likely to be one that aggressively dislikes risk-taking). While only a few small nations in Europe are as wealthy as the US, several more are close enough that the difference shouldn't matter. The problem is that capital is overwhelmingly unwilling to participate in venture investing.

The US not-so-secret sauce is: easy access to risk capital + a culture that has historically strongly encouraged entrepreneurial activity + a massive single market with one core language (that is also conveniently the global language of business, media and culture) + reasonable taxation and regulation policies + strong protection of property rights + ease of market access (low tariffs, low trade barriers, a foreigner can easily start/own a US business from almost anywhere) + very welcoming to foreign capital (few capital controls) + an enormous lead coming out of WW2 (which helped the US be the first to the tech epoch, which has buffered its lead ever since) + the global reserve currency + a massive traditional financial system (great for IPOs, stocks, acquisitions, leverage, etc. - it's why Alibaba is on the NYSE) + 19 of the top 20 universities on earth, and four or five dozen more that are world-class + a very successful university meets business development system (which has helped incubate countless new leading companies and technologies) + inexpensive energy + half a century of built-up knowledge, experience, specialization in every tech segment + a long history of immigration policies that allow people to come to the US and pursue their dreams (Japan and China, the #2 and #3 economies, have overwhelmingly shunned foreigners becoming citizens by comparison; the US tech industry wouldn't be anything remotely close to what it is today without the Andy Groves, Nadellas, Elon Musks, Jensen Huangs or Collisons).

That's the short list. It can't be replicated.