They mentioned that they wanted to avoid another pre-order debacle. But with this Target Fall Geek Out promotion it seemed like the possibility was there that Target might drop this one without announcing it in advance.
In actuality, I think that Target might want to make this an in-store only item simply because of the shipping costs. Once you get over a certain price threshold you get free shipping. Shipping a box that's big enough to hold the Blue leader X-Wing might be kind of expensive, even for Target. That could be some of the reasoning here. But as always with exclusives, they're designed to spur foot traffic into actual stores.