Two reasons FR won't try ABZ-STN. The B737-800 is frankly too big and domestic air travel is dying in the UK. FR killed STN-BLK / NQY and STN-PIK is now a single daily flight. The other reason is that STN is not a FR hub, it's a base. There is NO connectivity with FR, they are point to point only and won't let you book a connection even if you asked.