I guess cos you have to have 850+ hardcore enough fans to travel away on a Friday night, pay £22.50 for a shit view (that they all know about already) and not be able to get into the pub outside the ground*. So I reckon they won't sell out.
* I hope they don't bar them form the Sportsman, but they do usually.
NB, I would be delighted if they did, it would restore my faith in football supporters dedication to a degree, but I don't think it will happen.