As a retailer I would assume they probably need to move the products they have on their website first before customers move on to products that have yet to be released.
I don't think the pre-order links are hidden for purposes of SA commission or to encourage people to call in as they do most of their sales online.
Also, it's actually kind of easy to find the hidden links if you change the numbers around. I don't think there is any secrecy at all otherwise they would make it harder for people to find these links or wouldn't post them at all. I was able to find bags until the end of August just from playing around with the numbers including purple haze and many, many others.