It is easy to tackle safety issues like CFIT, mid air collisions, loss of control, and so on. They typically have a fairly obvious cause and affect. Fatigue is a bit more nebulous. It is often a contributing factor but rarely, if ever, a sole cause of an accident. It can therefore be shuffled down the priority list when it invariably turns out that fixing fatigue issues is commercially inconvenient. There is also the fact that a pilot must not present to work in an unfit state. Whenever fatigue rears it’s head the authorities can always just say that the pilot was at fault for not getting adequate rest or standing themselves down.