Well, to start with it was. The clue is in the name Air-Bus, it was designed as a short/medium haul wide body in the belief that people connecting from a 747 long haul flight would want "wide body comfort" (remember that?). It turned out that there were hardly any short haul routes that could support A300 operations without reducing frequencies and those that tried lost custom to airlines operating narrow bodies at a greater frequency. The project was saved by the advent of ETOPS and they were able to develop the thing into a longer-range aircraft, whilst busily developing a short haul narrow body.