I would actually argue that French literature is not better than any other literature. The same styles, plots and scope of literature can be found in many different writings which are not French. Some people think that French literature is better because they feel that the French authors are trying to share stories and experiences rather than trying to write for money or acclaim.
I do not personally think this is true though. There are so may incredible authors and works of literature that do this same thing. Some may try to quickly put a story together in hopes that they may make a lot of money, but I do not think that all of French literature only contains brilliant, and selfless works and many non-French works that are meaningful and wonderful.