Phileas - Blackpool is a completely different case - much quicker road/rail times from London and surrounding areas and not nearly as much demand from southerners for visits.
You have got it, I do see STN as a service for the tourists. 10.5k seats per annum isn't very many to fill for that purpose.
As for the comment about me not willing to pay a reasonable fare, you may note from a previous post I used to frequent the LCY route which was never a bargain I can assure you. I have spent much time in Cornwall during the winter. Not nearly as bleak as the Kent coast!