I never understand why people don't wear seat belts, even in cabs. I think the thought is that it's the city, you probably won't be going fast. But humans are really bad at judging just how fast they are travelling.

Imagine I asked you to absolutely sprint full speed into a tree while blindfolded. So no time to brace yourself or slow down. You'd probably refuse, thinking this will either hurt very badly or even permanently injure you in certain circumstances. And that is at 12-15mph for most of us. In a car you are going at least twice as fast at all times, and have all sorts of fun objects to break your motion, like steering wheels and dashboards.