172driver
It's not enough to be full, it has to be full with a decent yield. The airlines have not managed to square that particular circle.
If the experience of the merchant marine is any guide, we will eventually have two or three global carriers, along with a passel of 'tramp steamer' equivalent budget options.
Now would be a perfect time to make that change, because all the airlines are currently wards of their respective governments.
Unfortunately, airlines are such a small part of the global economy that they do not get much serious government thought.