Tommy,
When I go flying on scheduled services whether it be on business or leisure I want a suitable schedule, one big problem with loco one flight per day flights is that they fly when they want to and not at an optimum time of day to suit the passenger(s) ..... i.e. hotels have recognised check-in/check-out times, once does want to be arriving too early or departing too late!
If, by suggestion, there are a mere 4 flights per week and a Cornish local has a meeting in London to attend, perhaps a one hour meeting, then they would need to occupy 2 or 3 nights, at cost, in/near London, it just wouldn't happen, they'd take the car or train.
If someone needs to, let's say, travel to/from on a Wednesday but there are no flights on a Wednesday, they'll make alternative arrangements such as the car or train!
10.5k? Even 25 years ago there were more people travelling LON/NQY than 10.5k per annum, the HP7, five and two half days per week, let's say 32.5 pax per flight, that's over 20k pax per annum!