Because ....
They have all their eyes dotted and their tees crossed.
You are confusing working conditions with safety & operational outcomes.
They would have done all their safety cases, hazids and would have contingency plans in place. They have fatigue management systems and policies in place. Point to one thing that they are doing that is illegal. I'm sure even the one man doggo has been covered off. They aren't silly.
Now, consider ... what if the proverbial DOES hit the fan. I can only see the finger pointing at the troops. "But I was too tired after doing lots of overtime Your Honour"... "Did you abide by the employer's Fatigue Managamnent Policy, son?" ... "Ah ... but ..."
That's just one scenario. I'll leave it to you to consider every situation that could go wrong. Then consider what Airservices has in place to cover itself off. Then consider what you have in place to cover yourself off.
Oh, the working conditions .. that's another story ... there are ways to go about getting them re-modelled.