For me, it would take a bit of success. I am now trying to switch my career to something that could be done remotely because I want to move to Spain and their job market is terrible. But other than that, Spain is awesome.
I am from The Czech Republic and I love my country... except for the long dark soul-crushing winters. This affects me a lot. It is a surprisingly big part of quality of life. Spain is much more friendly to things I enjoy the most, like cycling, hot weather, and being outside.
And living in a foreign country for a few years has benefits. I have tried this before. You need to learn a lot of new things and that keeps you sharp and focused - I enjoy that. And somehow, I am not a person with strong roots. I love discovering new places, meeting new people... I could write a book about the advantages of leaving your home country.
I understand that for many people it would take something terrible happening to leave their home country. I just wanted to mention that it has great advantages too. Which does not mean that I do not love my home country, of course.