This. Why shouldn't driver assist be able to tell when the actual driver is drunk/tired/dangerously incompetent and pull over. It could even call their emergency contact or a taxi and disable the car.
Because no one would buy it. Who wants an inanimate object deciding that they are to tired to drive with no discussion or recourse?
And can you imagine the liability implications? "My spouse had an asthma attack/allergic reaction/severe cut in the of middle of the night and my car stopped me from driving them to the hospital. They died before the ambulance reached the house."
...and the reverse liability implications: "My spouse had an asthma attack and their car didn't pull over safely, so it is the [car manufacturer]'s fault that they crashed into a tree and died."
Not being a drink or erratic driver, I was thinking more of driving when I'm tired. It is possible to be a little too tired to drive safely without realising it, but I imagine the extra small adjustments you make when this happens - because you drift and correct - would be recognisable by the car.
It would be a huge pain if you are on a long drive and your car decides you need a nap! But it would save lives, possibly mine. Personal transport is a convenience. Personal safety is paramount.