The biggest reasons I see is that Europe is still a collection nation states whit each having it's own language, culture, laws and needs, EU hasn't removed those (yet, god forbid). There really is no single market for many services like there is in the US, in Europe you have to develop and sometimes apply for permits and licenses for each country even with the EU, since EU usually regulates retroactively not so much proactively.

The second is that there is nothing like the US federal government or military that could fund and/or bootstrap tech companies with contracts. Like google, SpaceX and Microsoft have both benefited massively from taking lucrative contracts from military government and US intelligence agencies in the past. Those allowed them to grow and consolidate first cover the US and then springboard themselves global.