Hurray, you have asked a very important question. Unfortunately there seems to be no concrete answer. Since the beginning of time people have been abandoning their birthplaces for foreign lands. About the only reasonable answer is that the human being as well as other species seem to be infinitely adaptable. Call it evolution although some prefer to call it revolution against their birthplaces. You are aware that many individuals do not adapt to their new environments evidenced by the large numbers of individuals who cannot live in a foreign environment, returning to the more familiar homeland shortly after arrival in the new. Again, survival of the fitest. There is also the fear factor, having made one major mistake by moving to a new land, some prefer not to make another mistake by returning to the old familiar one. Others live the proverbial 'life of quiet desperation' in hopes that someday their situations will improve allowing them to live between cultures frequently visiting both rather than living permanently in either.