It is was and always will be about total revenue being greater than total actual costs, including depreciation.
Following on ratpoison's line of thought, the railway train from Perth to Bunbury, ~77nm, fairly comfortable, business class type seating, food and beverage extra, Fare $30.50 = around $710 Per Syd. Around 90 minutes. And they make a profit.
Like the "air charter" business the airlines have for the lat several decades trained the public to expect ever decreasing fares to the positively ridiculous levels at which they are now.
They have now locked themselves into a death spiral as afar as revenue is concerned. If they increase the regular fares to economic levels and/including cancelling the idiot sub$100 specials, they will be forced to rely on the business fares which are actually also subsidised by the sub economic economy fares, they are screwed.
it is only the speed at which they get screwed that would vary.
I think they call airline finances Voodoo economics.
The chattering class would find Skype et al just as effective for family comms and much less stressful
.
There is no "right" to cheap travel anything, at least to subsidised mass travel, unless we vote for it, which would be a Pandora's box.