I appreciate that some people can't commit until the last minute, but to me, it's like leaving the turkey buying until Christmas Eve and then it being Tesco's fault they've sold out. The tickets have been on sale for weeks, available 24 hours a day online.
I'm not sure of the ramifications, but I'd imagine the away fans seating would have to be agreed with both the league and the away club in advance of the tickets going on sale. Perhaps even run by the Police and Safety Groups. I don't think it's an arbitrary decision that could be taken quickly by the club in the week running up to Christmas.
Coupled with the fact that many of the staff (both stewards and Compass catering staff) are students and may be away from Sheffield for Christmas, thus not easily recalled at the last minute, I think some fans ought to be a bit more understanding and take a little bit more responsibility for getting themselves organised.
Yes, it would be wonderful to have the ground full obviously.