Why do parents not supervise their children?!?!?

Today when I was in the car with my mum we were heading home but as we drove past this women with her head in the car we noticed her child running around unsupervised around the footpath. Obviously my mum slowed down and Just as she drove by she noticed the child pop right out of nowhere right next to the side of the car. This was unimaginably frightening as this child could have ran out on the road and been killed! So my question is WHY on earth don’t parents supervise their children! Particularly on a busy road!! Its seems to me as drivers are not only looking out for their safety but are also having to look after the safety of pedestrians!!