MOO, is that many "hot car deaths" are probably done, because the caregiver is just tired. Maybe tired of the crying baby, or toddler. They are in the car, in a car seat, and finally quiet, maybe even asleep.
It would be so tempting to just let the baby/toddler sleep. So that the caregiver can just have a break. And then, they just start doing things, and actually "forget" that the baby is in the car, or the length of time the baby has been in the car.
I am not giving anyone a pass on this, just that I realize how tiring it is to take care of a young child all of the time.