Because that's what they do every single year. You can go into the Supreme news archives and figure it out pretty easy it's not rocket science.
Why would they wait until 3 days before the drop to show the collection though? I would think that Supreme would want to preview it with time in advance in order to build hype for the pieces.
For both F/W 2012 and S/S 2012 the preview was the Monday/Sunday of the week before the drop, so chances are it will be up in 2 days. No it's barely the 9th, the preview won't drop till the Monday after this one. And that's gunna suck for you guys in the middle of no-where gunna have to wait an extra week for the drop then a couple more days for shipping.
Except that I already checked the archives, and though you are right about that for the years preceding 2012, that did not happen for SS12 and FW12. In both of those seasons, the preview was the Sunday/Monday before the first in-store drop.
EDIT: I misread, you're right.