It would be very hard for a country to force it's most ambitious to not leave if there are other places eagerly recruiting them.

But when such a pull exists, it's very hard to counter that. Consider the number of non-SV places in the US that have tried to replicate that environment and basically failed. Even the famously "business friendly" places like Texas or Georgia that are success stories for poaching tech companies or film production largely work by having companies move there once they've left the high-growth phase and are no longer chasing strictly the most ambitious would-be-best-and-brightest talent.

The success stories there (that aren't just resource-extraction) have come from significant protectionism, essentially forcing a country to build its own version of the mega-companies even if it's a money-loser with copycats building shoddy copies for decades at first.

There's no easy way for Europe to magically change that with "culture." There's too many already-established mega-talent-bases in other places to think you can have people just pass up on that in a fully-global-market situation.

I would ask instead: why let those foreign mega-corps be so integral to so many basic services of modern life?

Perhaps not just Europe, but the entire world, would be better off if we had fewer monoliths and more variations, with more flexibility for local markets to develop different solutions or in different directions.