There is a common metaphor that compares the good to the warmth or the light, and the evil to the cold or the darkness. Physicists tell that the cold is the absense of the heat, and does not exist. By analogy, people claim that the good is something that really exists, but evil is just the absence of good.
Why they think that the darkness and cold is the evil? A stone cannot be evil, but can be dark and cold. A chair cannot be evil. No inanimate object can be evil because of the lack of will. And everything that's not evil is good.
Inanimate objects have no ability to do good things. Still, they're good, so doing anything isn't required to be good.
Unlike inanimate objects, humans has the ability to do. I'm taking an assumption from the Bible that humans know good and evil. So a human can do evil things. All above means it's enough to not to do evil to be good, doing good isn't necessary.
The most of the universe is inanimate and cold. So, the good is much more common than evil, and less noticeable. And the cold is much more common than the warmth. You need to be close to the star to actually notice its heat. The cold is as common as the good. The heat is as rare as the humans, only the humans can be evil, thus, the heat is as rare as the evil. By the logic above, good does not exist, but evil does. So why does the metaphor compare the good to the warmth and the evil to the cold? People are burning in hell, after all. And devil is called Lucifer.