Why do Iranians rarely become refugees or illegal immigrants despite living under such an oppressive regime?

We all know the American border crisis. People from failed and authoritarian states like Venezuelans, Cubans, Haitians and recently the Chinese, crowded into the US-Mexico border and caused the border crisis. As a Chinese myself, my fellow countrymen even invented a word to describe their illegal immigration from South America to the US border.

But why do Iranians usually only immigrate under legal ways? Even the number of application for asylum in Western countries is not very large.

I also noticed that most Iranian opposition leaders still stay in Iran, not like supporting opposition movement overseas like our Chinese counterparts.