They want to find refuge from stress of living in a country where it is andheer nagri and choupat raj. They want to run from a place where you are not safe from criminals no matter where you live and no matter how powerful you are and no matter how much money you have . You can be victim of a crime even if you are dirt poor. Anybody I know living in Pakistan have been victim of some kind of crime. But here in US hardly few of my friends or family were victim of any kind of crime. They want to flee from a country where people say if you want to win a case in court hire a good judge , not an attorney. If you want a job you have to either bribe someone or you have to be connected to someone . Your talent and skills have no value. A country where a group of elders can allow gang rape of an innocent woman or girl for no fault of hers. A country where you cannot even get a grave or death certificate without bribing someone. A country where daughter of a chief justice is given high marks on exams by the chief of education board to save his skin. A country where everyday there is a bomb blast somewhere taking lives of innocent people. These are enough of reasons or you want me to list more ?
Spot on.
Actually, my family left in the 40s. Poverty is probably the main reason. Pakistan is extremely poor (its not all Defence!!), so most leave because of economic reasons. Minorities like Ahmadis and Christians leave because of persecution.