That's because once you have a runaway success the US will tax you lower and your quality of life will be higher than what you can achieve in Europe. The USA is a great country if you're on to a winner. So the vacuum cleaner in SV tends to suck the air out of a lot of EU successful start-ups and engineering efforts simply because that's where the money is. Typical start-up valuations in the USA dwarf those in Europe, access to a single unified and mostly mono-lingual market are far more of a factor than any EU regulations, that's just a dumb meme that gets tossed around by the clueless. Yes, taxes are higher. But so is average quality of life, as opposed to average GDP, which relies on outliers.