The axis being so far away, even if they are all the same, makes it difficult for the reader to line up where the peaks are, though some are easy to get from contextual clues (~1945 for War movies for example).
Think of thrillers more like rollercoaster rides - they’re fun because they’re exciting and sometimes scary
Horror is more like haunted houses, they’re fun because they’re scary, which is sometimes exciting
This is the interesting thing about genres - they’re often abstract and can blur definitions easily. The same way we don’t consider a hot dog or a pop tart a sandwich, even though you can often find the definition of a sandwich in each.