The US tech companies just dominate market cap compared to the largest European companies. As outlined by this article by Statista:
As the following chart shows, the power and financial clout wielded by the five companies often summed up as Big Tech is unmatched in Europe. While Apple, Microsoft, Alphabet and Amazon have market capitalizations above or close to $2 trillion, the most valuable public company from Europe is luxury conglomerate LVMH with a market cap of $411 million. In fact, the five most valuable companies from Europe combined, including two from Switzerland which is not an EU member but part of the European Single Market, do not match the market value of either of the four companies mentioned above.
Statista by Felix Richter