Because the universe is non-intelligent, non-designed and non-caring. There is no cosmic mechanism or intelligence that punishes the wicked. No good God exist.
That good things should happen to good people and bad things to bad people is only something that can be understood and caused to happen by an intelligent and compassionate being.
Some people do bad things: steal, murder, bully, etc.
Therefore, if we want good things to happen to good people, only we can make that so. That means we have to work together to defy the cruel indifference of the natural world, and create a world of compassion and justice.
"The only thing necessary for the triumph of evil, is for good people to do nothing" - Edmund Burke
Richard Carriers response