The concept of pre-orders was a solution to a problem, the problem being that shops could not keep up with demand for a product on release day due to its popularity. Thus Pre-orders came about, a practice which guaranteed the consumer a copy on launch day.
Pre-order numbers are good for the industry because it gives the developers and publishers an idea of the initial reaction to the game and how large production runs should be. They can also budget for how much marketing they’ll need based on early reactions and pre-orders. The retailer also benefits because they can be assured of minimum sales. But sadly, what should be a beneficial arrangement for all actually gives rise to certain questionable industry practices, specifically things like review embargoes.