The VAST majority of movies that have been made in the past (when the real indicator, % of population going to movies, peaked) deal with ordinary, realistic human stories. Murders are incredibly popular, of course, but so are fraught romances, coming-of-age, and grounded hero-quest movies (which even Bachelorette Party borrows from).
But your point is otherwise completely valid. They found out everyone likes cake, and converted their buffet restaurant to all-cake all-day!