*wham* *crunch* *ow*
I first encountered this alarming phenomenon in Taipei, while stepping off a bus. As I did so, a scooter zoomed by in the 18 inch space between the bottom step of the bus and the curb. I narrowly missed hitching a ride on the scooter by snagging my foot.
It looks like scooter riders go through the following thought process, which I hesitate to dignify with the term "logic": "I'm not a car, so I don't need to obey rules of the road for cars; I'm not a bicycle, so I don't need to obey bicycle rules; I'm certainly not a pedestrian. Therefore, I don't need follow any rules! Besides, I can dodge anything."
So what it is it? The more analytical part of me believes it's because in most places you don't need a licence to register or ride one of these things. Also, in most places where these devices are a significant part of traffic (Thailand, Italy, etc.) most everyone is in a state of denial about traffic laws, so it'd be a stretch to expect a scooter driver to pay them any attention.
The rest of me is just amazed I don't see more dead scooter riders strewn about the roads.