Phileas is of course quite right about the aversion to backtracking when taking any route. Go way back to the 60's and 70's and even then it was pretty hard to get anyone to book a flight which involved going over the same ground twice. Possibly no logical reason but it is none the less a major factor to account for when you understand the business.
When comparing the train with flying you must also consider the geography of Cornwall and the major conurbations. Look at the location of Newquay in relation to say Penzance where the train terminates. You would need an extra hour to get to Newquay before you start if you live that far West. I am relatively near to Newquay ( even nearer to Culdrose) but a taxi driver will say 45 minutes to reach the airport but I can be at Truro Station in 10 minutes - so it isn't that simple.
Flexibility is so important especially if you do not wish to night stop, one rotation a day does not allow the possibility of flying up for a meeting and returning the same day, in that case what is the advantage of flying over surface transport?
There is a solution as I have said earlier, I have already muted it to the right people but it would involve a lot of co operation and in the end is insufficient to prove whether or not Newquay Airport is viable in the long term. That is the bottom line of this thread surely.