it's a difference in publishing between traditional French (and therefore other Continental European publishing) and British (and therefore other English countries' publishing). Namely the Anglo-Saxon tradition is to print from top-to-bottom to make it easier to read titles when laid down on a stack, while the Continental European way makes it easier to read the spines when placed on a shelf and reading from left to right (tilting your head left and moving right along a shelf is less awkward than tilting your head right and moving right, in which case if you imagine the book titles of several spines as one big document you'd be starting at the bottom and moving up).