ALL of the above apply in one way or another but to me the single main base reason why we find ourselves amongst these pages watching QF self destruct for Eg is THE FARES ARE TOO CHEAP!!!!
I remember my first overseas trip back in 1985, when I paid I think about $2200 for a return ticket on QF to London.
Fast forward nearly 30 years to today and I reckon I could probably still pay the same, maybe even less, for the same ticket.