All out of excuses?

I mentioned to my wife on Wednesday, as I bought a 20 oz. bottle of Mountain Dew (the finest beverage in all Christendom), that when 20 oz. bottles went from $1.19 to $1.29 they claimed it was because of rising transportation costs due to the increased price of fuel.
Then, this spring they raised prices another 10 cents, as gas surged up past the $4 mark.

However, now gas is cheaper than it was when either of these price hikes occurred. Why can't I buy a Mountain Dew for $1.19? Seems like I should soon be buying my drinks for $1.09 as the price of gas continuing to plummet.

Similarly, airlines have been hiking up rates "due to rising fuel costs" for the last few years. The lone cheap airline, Southwest, claims it was able to sell tickets cheaply for a number of reasons including locking in $70 oil contracts years in advance. Now oil is trading at $50, a five year low. Shouldn't the airlines ticket prices plunge as fuel is now easy to be had? Shouldn't these airlines lock in oil contracts at this new (and probably unsustainable) low just like Southwest did before the price rebounds to a sustainable $65-70/barrel? Why aren't they doing this? Why are ticket prices staying constant or continuing to climb?

These companies are missing a golden opportunity to rebound their profits: lower their prices and increase the movable quantity of their goods.

It seems to me they are now profiting off the short-term memory of the economy. No one seems to remember why they raised their prices, they accepted the price increases at the time, considered rising gas prices a hopeless, one-way road, and never concerned themselves with the chance that in the future gas prices might decline and so too should commodity prices.

So if the prices aren't coming down, what's the excuse?