We have the concept and promise of reward in heaven.
Let's say a given person is born to a good family, does her school work, has a couple good friends, meets a nice boy, earns salutatorian at graduation, gets her liberal arts degree, raises 3 sons, enjoys grandmahood, and dies peacefully in her sleep.
When she arrives at heaven, what is she rewarded for? Because she had a nice easy peaceful life with no challenges?? Unfortunately for her, no reward for an easy life.
Wouldn't she then say to God, "Lord, why did you make my life so easy? Why didn't you give me more opportunity to show the excellence of my character?"
Another example - the highest military award is the Medal of Honor. Very few are given and rightly so. It acknowledges character, bravery, honor, fidelity, commitment, sacrifice, and brotherly love on level that very few of us are ever challenged to display.
You don't earn one without getting shot, and usually killed. The horror of war is the context wherein true greatness of character is rendered and experienced. There is nothing like it.
In like manner, natural evil is a challenge to us as human beings, but also an opportunity to exercise greatness of our own, and find out for ourselves what we are really made of - whether that be good or evil.