Like, imagine a successful-at-home French startup wanting to expand internationally. First, unless you're happy staying in the confines of the old French Empire, you're gonna need to translate everything, definitely to English, maybe to German or Spanish. Second, your app is built with French attitudes in mind. Chances are you're gonna have to change that to adapt to American, British, German tastes, and that's a lot of redesign. Third, for every country you expand to, you have to comply with local rules and regs. The EU has helped here, but definitely not solved the issue.

Whereas in the US, not only have you got 330 million wealth consumers under broadly the same legal/cultural regime, but they practically all speak English too! That gives US startups a much more solid base to expand from. Hell, in Europe the UK is by far the biggest tech hub on the continent, and Ireland punches far above it's weight. Don't discount the advantages of language or culture even in a globalised world.