Most of those countries were below living standards/salaries of western europe while having for some of them a very strong education system. Romania for instance trains a lot of good devs/it ops. All this qualified workforce can work in any country of europe. Add to this qualified workforce from syria/turkey for germany, North Africa for france and you see that while European companies did not grow like the US one, the pool of talent they can grab is larger than ever. the cake became smaller and Europe did everything it could toblock ambitious tech companies to grow and use the stock market as a wealth tool. they don't even understand that they operate in a global market and that if they tax or limit growth in their own country then the companies will move out. Dublin and Amsterdam for instance became hubs for this reason.
There is also the perception in the old world that being a "Techie" is like being a white collar factory worker. Developers are definitly not considered as stars in Europe. Most of the engineers in europe that want to make money work for an american company.