Good one.
Okay - let's look at a BN2 just as an example.
Assume £100 one-way fare.
Max pax = 9
Therefore max income per sector = £900.
It probably costs around £500 per hour block time to operate a BN2, including leasing costs, maintenance, consumables and a full-time driver (no catering).
Plus landing fees - assume, say, an average of £200 an airport.
Plus handling - is £50 per turnround reasonable for an aircraft that size?
Let's be optimistic and assume you can do the trip Oban-PIK in 30 minutes block time.
Your costs are therefore £500 for the sector.
Therefore, even on the most optimistic cost estimates and a fairly high ticket price, your break-even load factor is 55%.
Add into that office costs (including ground staff), set-up costs (including getting the AOC) which you'd have amortised over, say, 5 years, plus "hidden" costs such as initial and recurrent training and testing, uniforms, blah blah blah...
Add to THAT the fact that maintenance costs are going to be high for any aircraft kept on the West Coast of Scotland (sea breezes do wonders for corrosion) and can anyone see how the sums are going to be made to work?
Change the aircraft to, say, a Twotter and you've trebled your crew costs, approximately doubled your aircraft DOCs and only doubled your carrying capacity.