" crew were loosing focus and in an emergency it took too long to regain focus. "
Anything which removes from the driver feeling the need to remain in constant control and concentrating is a high risk.
Because there will always be a point when s/he thinks that they can put attention elsewhere for a brief moment. And if nothing catastrophic happen then they'll do it more and for longer in future. And so on.
It's not about driving as such. But about perception.