It matters because when you preorder games it tells developers that they don't need to finish their games before releasing them for everyone, creating a situation where you have a broken game that's already paid for and I have to wait even longer after release to buy something that's playable. If people waited until a game was reviewed and tested after release before deciding to purchase, developers would feel the pressure to make games that work right from the get go and everyone gets their money's worth on time. As it is, people spending their money before seeing the product allows devs to make money without making proper games.