Because they might be able to fill them more easily, or at higher yields than they are able to do at HUY. If they can't, I rather suspect they won't bother. Worth remembering though that KLM UK seemed to have no trouble putting bums on seats at both SZD and EMA which is relevant for 2 reasons. Firstly, full aircraft are no gurantee of longevity. Secondly, DSA is arguably in the centre of the SZD, HUY and EMA catchment areas and KLM might think a higher capacity operation from Doncaster might better serve that part of the world than 3 a day from HUY.
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