KLM: AMS is slot restricted and they had to drop routes based on feed to their international routes. No reflection on SOU as the AMS route saw circa 200k passengers last year;
KLM has many other UK destinations, but only SOU has been dropped?
Volotea: SOU was its only UK base so they are hardly known in the UK, they are also making the strange decision to re-fleet with the A319. Again no reflection on SOU;
VOE still have over a dozen B.717's in service, so they can't have been making bucket loads of money or they would have found a way. BTW, SOU wasn't a base and why is chosing the A319 strange rather than operating the almost unique B.717?
As has been discussed many times, airlines come and go at SOU and don't seem to stick - this must be a concern.