Not at all. By far the biggest engine of emigration is money. In my country (Romania) there are millions of people working in western Europe (2 million in Spain, 1 million in Italy, probably something similar in the UK + Germany + France). A large number of them are parents who leave their children at home and work for most of the year there to gather money.

Even if you're talking about just software devs, people still move to the west for higher salaries, though I believe there is more movement towards the US, especially since the software industry has a lot of local branches of US companies.

But I can tell you from the ground that at least the common perception is that you are generally going to be wealthier as a software developer in western Europe than in Romania, even though in Romania software devs tend to be much better off than the majority of the workforce (and even though software devs in Romania don't pay income tax on their salaries, which is a nice 15% rebate).

How are there 1 million Romanian workers in the UK(since brexit happened)?

I was saying 1M between UK, Germany and France. Most likely today there are fewer, because of Covid19. Brexit hasn't lead to repatriations, so no large change caused by it I believe.

1m total, not (necessary) tech workers.

I'm aware, but that's not related to my comment, unless you're actually claiming that programmers have lower standard of living in the western Europe compared to eastern Europe (which I believe to be false).

Belarus, Ukraine, Russia have low taxation for the salaries in IT (https://en.wikipedia.org/wiki/Belarus_High_Technologies_Park) To have your own 2-3 room flat in Minsk (Capital) by the age of 35 is pretty common for Belarusian programmers and basically unheard in the West. So yes, I can argue that programmers can have higher standards of life at home than your typical "tech hub" like London, Munchen or Dublin.