Mechanical failure is a fart in a hurricane compared to human factors (distraction, alcohol, run of the mill stupidity) when it comes to dangerous things on the road. Regulating mechanical condition is exponentially less effective once you start caring about more than the most basic things (e.g. heavy trucks with bald tires). That's why a handful of states have created then scrapped vehicle inspection programs. I get that it bothers people but mechanical failure is a tiny edge case compared to everything else. Why bother, there's other better things to spend our resources regulating if road safety is the goal. If mechanical condition mattered more than trivially this would be reflected in insurance rated between states with/without regulation covering this (inspection programs).
In my experience shitboxes with mufflers falling off and rust holes are more likely to damage community image than anything else.