This is because screenshots are not enough evidence to ban players off of. They can be taken at the wrong moment or photoshopped, and staff need to be completely sure that someone is actually breaking the rules before punishing them. Picture this: two players are in combat, and they both stop to eat at the same time, and are not hitting each other. You snap a screenshot, and they are falsely banned because the screenshot was taken out of context. Or this: a player is jumping from a high place on a map to sneak attack another player. That player gets a screenshot of the other person falling, and they are falsely banned for fly hacking. Or this: A person photoshops a picture of someone floating in creative mode on a private server into a picture of a cubecraft lobby, and adds a player's name. That player is falsely banned because someone faked them hacking. This is why we cannot accept screenshots for non chat based offenses.