The people getting them early are the ones who ordered the most popular models. Think about this from a logical standpoint.
If you have an order for 74,581 sports, 18,274 SS (say 500 of this are the SS Space Black) and 4,684 Editions then the logical thing to do is focus effort on the sports first and foremost.
Not only that, but also, when companies like Apple start a production run for the 74,581 sport pre-orders they are not going to make exactly 74,581 watches. They will round up to the next "batch size", so for example they might throw out 80,000 sport models in 1 single go which means some of the late orders get theirs early.
People who ordered from the smaller batches (like our 500 watches in the example above) will come last in terms of manufacture.
With the sport they are chucking out just 1 SKU in 2 sizes (ignoring the SG), so they can make millions of them, slap on any band, pack it up and off it goes. With our watches there is no other watch in the line like it. Yes the link is the SB's baby brother, but the SB has to get the DLC applied which is an additional step which only our watches go through. This means production takes longer.
Everyone is talking about production issues, etc. who said there are any issues. Just more likely that logistically speaking and from an engineering standpoint it makes sense to focus on the smaller orders of these more difficult to make watches after the bulk of pre-orders have shifted.