Preorders have nothing to do with it. That's just something stores are doing in the hopes of securing lots of sales and on the other hand eager customers do in the hopes of securing one product from the first batch. The NDA is only fair as it allows all reviewers and other such operators to have an equal chance. Some receive a sample earlier, some later. If there was no NDA, the lucky earlier ones would catch all the attention and traffic. From the manufacturer's pov the impact is bigger when it happens all at once and is not diluted over a span of time. Nothing forces anyone to preorder before reviews are out. The only ones that absolutely have to accept such a risk are the stores that have ordered batches of stuff to sell.