"Is God willing to prevent evil, but not able?
Then he is not omnipotent.
Is he able, but not willing?
Then he is malevolent.
Is he both able and willing?
Then whence cometh evil?
Is he neither able nor willing?
Then why call him God?"
Usually the answer is free will but then the problem of determinism comes up. Much of life is determined by accidents of fate. Where one is born, what culture, what time, what people they happen to meet, and many other variables that make free will just another part of the equation. And of course there are natural disasters and animals suffering as well.
Then this usually gets to the "fall of Adam and Eve" but then questions of whether one should be judged on their forefathers and previous generations comes up as a problem. In human courts it would be an injustice to punish a child because their parents broke the law or even worse because their great great grandparents broke the law. That would be unjust.
Darwin made this argument how natural evolution makes more sense with the immense suffering than a benevolent God.
"That there is much suffering in the world no one disputes. Which is more likely, that pain and evil are the result of an all-powerful and good God, or the product of uncaring natural forces? The presence of much suffering agrees well with the view that all organic beings have been developed through variation and natural selection." Charles Darwin