The camera was not actually used initially. With the old Autopilot software, attention monitoring was (and still is?) exclusively done with steering wheel torque sensors. Our camera got enabled when we purchased the FSD upgrade. I do agree the software is good, however: it's both more effective and much less naggy/annoying than the old "hands on wheel" method.

It still falls back on the torque sensor (requiring hands on wheel) if it thinks you're not paying enough attention, or if it can't see your eyes for whatever reason.

And I guess Tesla must have enabled the camera for all new vehicles now, at least in Europe, given that it's required.