Because suffering is a subjective point of view? I know that I'm not that well off, but compared to others, say of some African tribe that is struggling to hold onto indigenous identity and encroachments of Western society, I know that in the grander scheme of things I really don't have it that bad. There are even accounts of Jews in Holocaust camps that instead of reveling in self-pity they tried as hard as they could to comfort others, even if it meant giving their daily "food" to another person.
It should be apparent to everyone there is no cosmic justice. There is no such thing as a "just world." But things that happen just happen, for one reason or another. What we call suffering exists only because one person looks upon another and draws comparisons. Without this notion of us being able to compare, our-selves to another, or even some stranger to another, suffering cannot exist. We can feel pain and isolation, but the very idea of suffering is dependent upon our ability to compare.