Numbers... The disparity in population would certainly have placed the number of aristocrats at a much lower level than the number of people fleeing Syria today. Not to mention that many of these elites would have already been able to easily travel to Western Europe as well--provided that this would be the primary destination for them (I'm not yet familiar with any eastern route migrations of people going to the US). One more HUGE thing. These are aristocrats. If they're fleeing before their wealth is taken or unable to be sold, they're well off and able to move much more easily than a rather poorer country.