Biergarten and most of the other WS TS locations were having issues several weeks ago for late November, early December bookings. After several attempts of communication with CMs, using a variety of methods, a dining CM confirmed that it had something to do with holding back times for CP packages. Strange thing was that come my 180 +10 morning, all of my dates became available, so I managed to get Biergarten and Chefs de France dinner ADRs.
I am thinking it is another glitch, personally. If it they are holding back for CP packages, then why did late November and early December open up for me and a few others chatting on the boards. My advice, just keep checking back and email Guest Services.