I think that's how human brains be. We're already notoriously bad at correctly accounting for low-risk events (eg the lottery). Plus being constantly aware of the full myriad of threats we face would probably be debilitating.

If you haven't had or seen a kind of accident you're brain probably sees no compelling reason to account for it. My partner was lax about flu shots until she started working at a funeral home and saw how many people of all ages die of the flu. Now it's a threat she has the awareness to accurately account for.