One reason might be that many pilots are not effected in the same way by brutal rosters.
Eg, when I was 25 and very fit with zero responsibilities apart from my role as First Officer and paying the rent on my one bedroom apartment downtown, I could do these rosters no problem at all. Now, twenty years later with command and three childeren under seven, I struggle. I do an early (5am) two sector 12 hour duty and when I get home ( 14 hours after I left) I still have a lot that needs doing. When I get one of my 8 days off a month ( often single days off)I now sleep rather than mow the lawns or take the car to the mechanic. It’s not sustainable if you dare to raise a family and actually want to do things with them.
So it’s different for pilots at different stages of life. Management think “ we’ll if pilot A doesn’t call fatigued on that roster why should pilot B?” I’ll give them a clue, pilot B can’t go home to a quiet dark flat and sleep the entire time between shifts.