Can I ask why 'y axis pointing up x axis pointing right' coordinates system has such cult following with anyone who wants to use box2d?
What's your question exactly? Box2D defines it's initial coordinate system as y axis up and x axis right, as it's used in most of all cases in mathematics and physics.
SFML uses a y axis down and x axis right coordinate system, because images are defined that way (top-left point = (0,0)).
Those are all formalities and design decisions, it's easily possible to convert from one to another system.