the Muscat extension dates back years - back to when Oman Airways flew F-27's and leased small 737's
To get there you normally flew Gulf and changed
BA offered a non change 1 stop
Oman Airways expanded and put in a nonstop UK flight
Presumably BA still make enough (from people with Gold Cards??) to make it worthwhile continuing what is a rather odd service these days
I have noticed that Flight crew on this flight switch in AUH and the cabin crew continue to Muscat....for some reason.