My guess would be that love and money are the two main forces that have influenced voluntary immigration in the past (and still do?). Moving overseas for economic opportunity has always been acceptable - it's the reason we don't even question why people move from economically disadvantaged countries to the more wealthy parts of the world, such as North America and Europe, where supposed opportunities for "a better life" abound. And love will always be a driving force that causes people to nod their heads in understanding. It's our universal Shakespearean need for drama and grand gestures.
But for other reasons? Why?
I understand it, certainly. There is such a thing as love for a place and a life that just seems to fit. Happiness is measured by so much more than just love and money (though they can certainly help). But other factors can be so much less tangible, or less relatable, because they vary from person to person.
My friends over here understand that, and it's why we sit around talking about, for hours on end, whether we will stay. There's a love for this place, but there are also frustrations, and sometimes we wonder, is it really worth it?? Add love or money to the calculus and it would probably tip the scales strongly in favor of staying, but without it, we can only rely on intangible gut feelings that tell us that right now this is the place to be, and maybe later it won't be, but right now is simply right now.
And there's also something sweet and reflective about even being in a place, and a time in our lives, when our conversations can keep coming back to these topics. Because isn't it a privilege to be able to make such a decision independent of any external pressure, and to have the time and luxury to chew over the many paths we can choose to take our lives in, and then to say, "you know what, I'm really happy where I am right now, and that's all I need."