My "guess" is it's a high end binding and not a lot of kids get to spend that kinda money on bindings. So if stores can't sell them there are stuck with the cost and/or have to discount them at the end of the season to sell them, again losing money.
Just my thoughts
Also Flow Large start at US size 8 to size 11 if I recall correct
Slyder: I know that they start at size 8 (which is my size), but I currently have a pair of NXT ATSE in large, and while its not a big problem I find that there is quite a bit of space between the sides of the binding and my boots, thats why I was thinking of going with a Medium size.
Wiredsport: that might be it then, just wondering cause Ive seen a couple of sites listing them as sold out.