There are a whole host of BA franchise services not serving the London market in northern Europe and South Africa if you care to research.
I've often wondered who would want to fly one-stop to Muscat or Doha when there are non-stop alternatives available unless a lower fare was offered
BA has some very valuable corporate contracts into/out of the Oman however the back of the bus (Normally a 77E or 772) just isn't there.Therefore the rather rare tag.
There is no way those contracts would be handed to Qatar anytime soon (Some are a rather rarefied military nature)
I would also add that whilst Qatar onboard product can be world class that airport currently in use at Doha is a bl**dy awful transit point.