A LCY quick route filler to NQY would be a lot quicker and cheaper with some income than setting up a new continental route, so i guess thats a potential reason- it was good enough for a LGW 734.
BA from LGW used to leave with under 20 passengers some days on a B737 in peak summer, also LCY lost money for Air Southwest, the local operator. To be honest, CFE could make WAY more money elsewhere than a marginal niche route to Cornwall viable during the school holidays alone. Domestic flying is dying in the UK not expanding.
LCY leisure routes are niche into France or pricey holiday destinations with CFE. To be utterly honest, why fly when the train makes more sense from LCY?
BA- LCY-NQY-LCY E170
U2- MAN-NQY-MAN
EI- DUB-NQY-DUB (EI Regional)
EI- ORK-NQY-ORK (EI Regional)
BE- I think will operate Manchester
easyJet can sell more on board products on a longer flight than a quicky to Cornwall and back so the aircraft would more likely be better served elsewhere. DUB is a possibility with Aer Arann I agree but more than likely a lunchtime single daily return.