Airlines buy their fuel way in advance of use trying to hedge the bet on price increases. Unfortunately fuel costs don't drop for them as fast as they do on the market. But yes, one would expect the price of a ticket to reflect the cost of actually flying, but if the sales are strong, there's no reason to drop fares.

Years ago (and I'm sure still) the local water company needed to raise their base rate to cover the reduced usage due to a water shortage. Funny thing they didn't drop their base rate once water became more available. Called free enterprise? Once one competitor starts stealing your customers by dropping prices, the others usually follow suit.