The other issue is catchment area. How many millions or even thousands of customers are within an hours travelling time of the airport. That is why Manston could never succeed, and it tried so many times, because there just weren't enough customers within it's area to give it critical mass.
Southend is working just and it has, if my memory is correct, a population of 5 million within an hours travelling time, plus an integrated railway station with up to 8 trains an hour to London.
Perhaps Bournemouth airport is just in the wrong place to attract enough farepayers.