We live in a free and open society, and that means living among the uncaring, impaired, or inferior (among others). Unless you prefer some alternative with ongoing testing to make sure everyone is OK at any given time, this is a cost of freedom.
We all have 20/20 hindsight and can point at what seem like obvious signs that someone should have stepped in and "done something". But the signs aren't really that obvious (except in hindsight) and many appear in otherwise OK people, so looking for them would lead to a staggering ratio of false positives. As for stepping in to do something, who, when, and by what authority.
So we live with an imperfect situation and often the first reliable indicator of a problem is a fatal accident, just like the first sign of a serious (treatable) brain aneurism is stroke and death.
ON the bright side, these kinds of events are rare, which is what makes them "newsworthy" in the first place. Life here is pretty safe and countless people live their entire lives without any 1st or 2nd hand exposure to serious accidental trauma from any source.