Facebook has been so shady and unethical with their handling of violence and graphic media. They don't care if Facebook becomes a haven for hate groups, but report on violence and ethnic cleansing and they just might have to ban you.
Same reason tons of people are garbage. They prize order over justice, and don't make exemptions when someone is rocking the boat because the boat is sinking and they need to be rescued.
There are simply way too many users for Facebook to keep up so they over rely on people reporting "bad" posts and shitty algorithms. Posts shouldn't be removed until they are reviewed by actual people who actually know what they're doing.