kapusta – I think I know the answer to that one.
When it is a small child who needs to be buckled into a car seat, then the car seat is attached on one side and it’s usually not moved from that spot. If the car seat then happens to be located on the traffic side of the car, it is more difficult to buckle the child in from the opposite side – the sidewalk side. One must stretch across the car or actually climb into the back seat with the child to buckle him in. In that situation, the convenient, but less safe way, is to buckle the child in (as quickly as possible) on the traffic side.
That is the reason, but I agree with you that if it’s a choice between convenience and sakanah, choose inconvenience!
Now that I’ve gone into the long answer, I sure hope you weren’t just asking a rhetorical question!