because it's the last session. it's the most important, so we should save it for a time when all players should be able to make it.
Edit: Flatus has confirmed that he can't play next wednesday. If anyone else can't play, you should say so asap. I've been going on an assumption that more would find this date inconvenient for Eu2.
It might be unrealistic to hope everyone will be around the following week also, but it's worth a shot. Would everyone be able to make it the 29th? I wouldn't want to delay the game and then have somebody else have to miss when they would've made it on the 22nd.
Lets just see who else is expecting to miss these dates, and we'll go with the one that has the fewest projected absentees.
If somehow there aren't enough people planning to show up to either, we can always wait til the 5th of January as a last resort.