Movie genres surprisingly have a supply and demand factor as well as material things. Producers want there movies to come out at a time when people are off work or school. Most movies are released on holidays when the film makers know that people will be available to spend their time in the theater. There is then a demand for movies around Christmas, summer break, and other such holidays.
Therefore, for each seasonal demand, the movie industry must supply its audiences with an entertaining movie that fits the consumers demands in order to make money.