Because Bill took like 300 copies out of the system for GenCon. They sold out 300 copies of Wilderlands last year, by Saturday, if I remember right. So Bill expects to go home with zero copies left over of RA:R.
I do NOT know the exact number Bill is taking to GenCon, but at least 300 is a good guess based on how many Wilderlands they had last year.
So RA:R is as sold out as a 1,000 print run can be at this point. From now on anyone who wants this is going to have to make due with pdf and printing it out themselves. Which really isn't a bad thing.
With the exception of the few in the Alliance and other channels, which I imagine are mostly, if not completely, pre-orders made through LGS' that were sent through the channels soon enough to be honored by White Wolf/Necromancer.