Because, it is not for a lack of will-power, willingness, strength or effort. It is because they are overwhelmed, the damage becomes too much and they have no choice — they simply break. We can not determine what will damage and break others, because what may not damage us, may break others.
It is why I wrote The Damaged and Broken Stories. It took many years to learn, that for every one person who overcomes their demons, there are hundreds, if not thousands, who do not. Instead of self-righteous condemnation, perhaps, without judgement, we can show compassion and offer help in lieu of empty promises of what may be perceived as false hope to our fellow human beings.