After finding an issue with Keg Brawl, ArenaNet has disabled the mini-game until it has been fixed. Those that queue up for it will be taken to the PvP Lobby until then.
We found an issue with Keg Brawl and had to disable it. When you try to enter a game of Keg Brawl you will be taken to the regular PvP lobby. We will activate Keg Brawl again once we fixed the existing issue. Sorry for the inconvenience. [Source]