Peter , many of the flights are business flights.
I know they are... and I feel sorry for those forced to use them. Anecdotal evidence from colleagues is that when a proper door to door fully adsorbed cost comparison is done when booking anything from 4 to 1 week in advance then there is little or no difference in cost between any of the cheapie airlines and BA.
The "sucker" prices advertised are only real, to typical business destinations, when booked way in advance, impossibly so for most business users.
Fortunately none of the cheap airlines fly from Southampton, so it is easy to justify LHR and BA. If FlyBE offered a Southampton / Frankfurt or Zurich service I'd use them. But they do not.