In France, high school is divided in a number of tracks. Firsst there are “general” tracks vs technological tracks. Then the general track is subdivided into so-called “series”, each with a strong emphasis on some subjects : L is literature-oriented, S is science-oriented, etc… Then there are subdivisions : for instance litterature and mathematics, litterature and music, litterature and languages for the L serie.
There aren’t only just small differences between these series. Someone with a science specialization might have 4 or 5 times more math lessons than someone with a litterature specialization, for instance.
The “baccalaureat” (end of high school final exam) is a big deal in France. As a result of specialization, the exam in a specific field will be much harder and will weight more in the final result. For instance for the mathematics serie, maths and physics might have a weight of 5 while say, history will only have a weight of 2.
Within the L serie, the most common sub-serie has French and Philosophy as main disciplines, with the highest “weight”. So succeeding or not at the exam as a whole will be highly dependant on succeeding or failing in these disciplines. And it so happens that for some reason, and for all series, the French exam takes place one year before the end of high school, contrarily to all other disciplines. As a result, for pupils in the main L serie, since they already got their final grade in one of their two main disciplines, what is going to matter the most by far during the final exam is their grade in Philosophy, so they’re likely to be invested a lot in studying it.