Despite France being renowned for its cuisine why do most French people eat junk food daily?

France is a country that is well renowned for its rich cuisine which is embedded in its culture and history. However it seems that the eating habits of the French population have changed significantly over the last 30 or so years. I remember watching a documentary that was made 30 or 40 years ago about French cuisine and the average meal of a typical French family. Nowadays it seems like most French people consume fast food and junk food not just imported from the United States but also local junk food. This is interesting because France doesn't really have massive fast food chains like the United States does. Why did this shift in eating habits happen? Is this a generational divide?