Yeah, "we" don't ignore them at all. I'm not sure I'm able to articulate all the costs and efforts around road safety, but I'm quite certain it's... real high. Not just the directives of the NHSTA and the effort required to comply with them (crash testing and research, etc.), but most law enforcement activity (and the support laws and codes restricting driving activity), driver education and licensing (on passenger and carrier levels), road maintenance including pervasive safety features like guardrails, breakaway posts, collision barriers, road re-grading, safety signals.
Maybe the reason it could seem to someone like "we" do is exactly because it is so pervasive. It's second nature to get used to all the safety measures that surround us on the road. It's not that we ignore the danger of road accidents or their consequences: it's that the attention we pay to it is so constant it becomes background noise--humans notice novelty, not stuff we're used to.