I think part of the problem is if they provide a game, even for free, then they are responsible for the security of that game. Even if not legally, they don't want an article saying "unreal hacked by Ransomware people infecting anyone who joined a public server, people could download the game on the Epic store for free"
At least if a third party provides it then it's not really an official copy of the game.
At least if a third party provides it then it's not really an official copy of the game.