It would prevent players from going through the inconvenience of starting a game and then being kicked after 30 minutes. I'd rather not play at all than that. Not everyone knows about the bug. Alternatively they could also add a warning to the game selector but still allow players to play.There is no gain of putting it into maintenance
Also it would allow players to notice when it is fixed. They can make a forum announcement, but not everyone reads the forum.
https://www.cubecraft.net/threads/put-uhc-in-maintenance.201483/