I think they are sold without the duty (the sin tax), but still with VAT for an EU flight. Then add on the cost to run a shop in an expensive location.

Comparing a basic Gordens gin, at Copenhagen Airport it's 6DKK (€0.80) less than at a typical supermarket, 165 vs 171DKK/litre. However, the price in Sweden is about 260DKK/litre, and I assume the target market in that airport is Swedes.