Deleting evidence of a player hacking is a major issue. If someone were to delete all their videos and those players would dispute their ban afterwards, they would all need to be unbanned since there is no valid evidence anymore of that player actually hacking. And letting hackers who had been banned before come back onto the servers is one of the last things we want to let happen at the moment.
I would also like to point out that it's not like "Oh look, the evidence in that report abuse went missing, let's instantly perm ban the player who submitted the report now". When we find out that evidence of multiple reports submitted by the same person is not available anymore, we will contact that person first asking what happened to the evidence and we will try our best to retrieve it if possible. It has happened before that people their YouTube account was deleted and therefore none of the videos could be accessed anymore. We do understand that this can happen and we will try to find a solution together with that person to retrieve most of the evidence, if still possible. If someone ever wanted to remove all their hacker videos from their channel for whichever reason, they will need to contact a member of Staff so that they can be re-uploaded. But if someone purposely deletes evidence without notifying one of us, they will be spoken to and be dealt with if needed.
Also, since a few months ago, for this exact reason, people now need to sign an agreement in regards to keep their evidence available at all times. When submitting a report, it's your responsibility to take care of the evidence. It's impossible for us to re-upload every single hacker video that is sent to us. By signing the agreement, you let us know that you are aware of the rule and in case the evidence went indeed missing, we can look into a solution with you. If you didn't sign the agreement, then it's your own fault in case you are punished. It is clearly mentioned and visible on the template. We will still look into it with you, but chances are slim that the evidence can be retrieved then.