If people are consciously modifying their car to defeat obvious safety systems, I have a really hard time seeing how the auto manufacturer should be responsible.

I guess the probe will reveal what share of fatal accidents are caused by this.

Well, it doesn't help when the CEO of the company publically states that the system is good enough to drive on its own and those safety systems are only there because of regulatory requirements.

GM's Supercruise (which is the actual king of the hill for L2 systems) uses cameras to track the driver's eye position to ensure they are paying attention. It's significantly harder to defeat, is geofenced to prevent use in incompatible situations like surface streets, and has a much more graceful disengagement process. Most of the time autopilot is smooth, but sometimes it just hands control back to the driver without warning.

Teslas can famously be tricked by wedging an orange between the rim and spoke of the steering wheel to produce enough torque on the wheel to satisfy the detection. There are enough videos of it on youtibe that tesla could easily be found negligent for not doing enough to prevent drivers from defeating a safety system given that alternate technology that more directly tracks attention is available and tricking tesla's detection method became common knowledge.