For the same reason that many Indians (from a reportedly secular Third World liberal democracy) and Chinese (from the formerly dogmatically atheist land of Market Leninism with Chinese Characteristics), for instance, come to the USA to work, for instance. France, having been a capitalist empire, is far richer than Iran. If you have a lot of formal education or a great deal of uncommon talents like Marjane Satrapi's artistic gift, you are likely to make much more money in the West than in Iran or anywhere else in the South for that matter. Being richer is not the same as having "better culture" or "more civilization," however, and that's what Satrapi is saying, against ignorant interviewers who insist on feeling, and making their audience feel, oh so superior.
This false superiority complex -- the West is not just richer but also better in all respects than the rest -- is the structure of feeling that helps reproduce racism (whose existence in the mind of a great scientist recently brought him low) and imperialism. -- Yoshie <http://montages.blogspot.com/>