I'd say Said was cleverly associating his target with a term that was already falling into disrepute. Geographical shifts in scholarship may also have contributed, Asia being Asia wherever you are, but "Orient" making little sense if it's to your north, south or west.

My parents were of Norwich's vintage but I don't recall encountering either form in childhood except in "We Three Kings" (which I think left us all initially puzzled) or perhaps in period TV dialogue, and thereafter it was already perceived as old-fashioned, so I think Said was using that to his advantage.