I think the words City and United are synonymous with our respective clubs. There is generally no need to prefix either with Manchester. Other Citys and Uniteds are known by their town names. E.g. Newcastle, Exeter, Norwich, Peterborough etc. Occasionally, they are spoken in full, but that is usually when there is another club from the same city - Bristol, Oxford. On rare occasions the full name is used outside of these conditions - York City and Cambridge United as examples.
But when anyone says City, or United, it is accepted that they are referring to the Manchester clubs. This habit of always using Manchester United in full must be because of some insistence or directive from the club itself. Maybe they are worried that the rules that apply to food marketing will transfer to football clubs, and they might have to drop the Manchester from their title and become Trafford United, or Greater Manchester United. We can but hope.
