In the post-smoking hole enquiry, it is easy to say through toxicology that a pilot had alcohol in their blood stream. Fatigue is much more difficult to prove.
Companys like the fatigue argument because, if a pilot rings up crewing and says I am fatigued, Whoops there goes the career. If you do have a crash, well it's not the company's fault as the pilot should not have flown in accordance with the ANO. Also how do you prove it?? was the roster they flew legal? Aha the "Too Difficult" argument therefore the result must be pilot error.
I must admit that I do get fed up from non-aviators who do not experience 12 hour days with constant disruption to sleep patterns making comments on something they know nothing about. Having worked on building sites and on power stations, I know what hard physical labour is, but it is the mental tiredness that is hardest to cope with and will ultimately lead to fatalities!!