That, and also "sunk cost" - a wife, three cats, a sinecure at Johns Hopkins and the like. You see, I have not had a truly permanent residence since I turned 16 - I lived a few years in China, then back to my home town (Gdansk) to finish HS, then left for college, then Austria, then Michigan, then California, then New York and now Baltimore. Each change of scenery comes with a price - finding a new residence, new friends (OK, the internet created some portability in this department, but not all my friends are my keyboard pals), new surroundings, new culture, new language. I love to travel but as I am getting older, the price I have to pay for a nomadic lifestyle inconveniences me more and more.
Besides - Western Europe, which is where I would like to be, may welcome tourists, but not immigrants. So facing a choice between a country with a shitty political system and a more-or-less open door policy, and one with a markedly better political system but an "Auslaender raus!" attitude - I take the lesser evil route and opt for the former.
And then, there is the immortal Cavafy:
"The city will follow you. You will roam the same streets. And you will age in the same neighborhoods; in these same houses you will grow gray. Always you will arrive in this city. To another land -- do not hope -- there is no ship for you, there is no road. As you have ruined your life here in this little corner, you have destroyed it in the whole world."
http://users.hol.gr/~barbanis/cavafy/city.html
And hope? This reminds me of a story I heard in the old country about a Jewish guy who was hiding from the Nazis in occupied Poland. His hope was that England and France would defeat the Nazis. The poor fellow had practically no contact with the outside world, so he had no idea how the war was going, but his hope was the only thing that kept him alive. One day, however, he overheard that France fell and Nazi troops occupied Paris. This was the end of civilization as he knew it. His hope gone, he hanged himself.
The moral of the story is that the poor fellow erred by putting all his eggs in one, the most cognitively conspicuous at the time basket. Paris might have been the center of civilization as it was known ca. 1939, but the tables of war turned in the obscure city of Stalingrad that most civilized Europeans could not even find on the map prior to 1942. So even if our Paris falls, and all the hope is gone, we still should keep going, cognizant that after Paris, there will be Stalingrad. Hopefully, in our life time.
Wojtek