They asked the youtubers not to post videos of the treasure room(they can post about their loot) because they want to give people a reason to watch the stream. They wanted to show it off at the end if you recall DeeJ saying : "Can we get a key?" (You get a key after defeating the last boss on round 5) and Matt said: "Negative" as the mechanics of the game doesn't allow you to just receive a key and go drop down to the treasure room as the key must be redeemed once after the final boss and right in that game session.