I don’t think answer to this question, @mazingerz88; what makes a film a “hit” at Cannes or any film a “hit” anywhere is ephemeral. If filmmakers knew this they would make these films. No one sets out to make a purposely bad film. If there was a formula only good or great films would be made. Perhaps your best bet would be to watch all these films and figure out what they all have in common. If you can figure out what, for example, the following films have in common, then you have your answer! And if you do figure it out, you should move directly to Hollywood, right away, do not pass go! You will have the magic answer that has eluded everyone since they started making movies!
Padre Padrone
Under the Sun of Satan
All That Jazz
The Working Class Goes to Heaven
Pulp Fiction
Fahrenheit 9/11
Elephant
Dancer in the Dark
Uncle Boonmee Who Can Recall His Past Lives
:-)