Nakata, does it really need explaining?
You have presented a list of failures from across the ages - of the airlines that still exist, do you really think they withdrew because they were making lots and lots of money?
You also say no airlines were representing and then contradict yourself by immediately following with 'apart from...' Thomson and Ryanair - who unless I'm mistaken make up the vast bulk of commercial flights?
The simple fact I'm afraid is that Bournemouth's current offer is probably about right - catering for local need on key leisure routes focussed around the key summer peak and a little bit of winter sun/ski. SOU is on hand for nearby high-frequency key business routes, the London airports aren't that far away for everything else (also Bristol for more westerly parts of the catchment). I can't really see what else would feasibly work that you don't have, except for the odd incremental increase in leisure routes at say an extra weekly flight or two to Turkey or a Greek island.
If you were chief exec of an airline other than FR/TOM and your head/cash were on the line, what routes would you add?