"The airport operator and airlines know where the passengers who travel through ABZ/EGPD are going to."
Really?
I travel to Alicante 4/5 times a year - since the demise of Globespan I go through BHX, LTN, LGW etc and book the cheapest onward connection, usually Flybe from ABZ, then Easyjet, Monarch, BMIBaby or whoever. I check the fares at Skyscanner.net which then sends me to the individual airline website - I don't see how anyone at ABZ can know my final destination, and I know I'm not the only one who books using this method.
Yes but that's not the point I was trying to make, we're talking about commercially viable volumes, I'm sure there's any number of people designing their own specific routings to all sorts of places but I doubt very much they add up to enough to run a route at a profit to anywhere?
The majority of passengers book to final destinations using the carriers mentioned and the final destinations are well known.