https://www.gamespot.com/articles/amazon-prime-kills-its-20-off-video-game-pre-order/1100-6461276/

Amazon has announced that, effective August 28, Prime members will no longer receive 20% off of video game pre-orders. Instead, the online retailer will implement a new benefit that gives customers a $10 Amazon credit for pre-ordering select games. Depending on how many games that ends up being, this could severely cut the savings Prime members receive when buying new games.

Amazon has offered the 20% pre-order discount since 2016, effectively bringing the price of a standard $60 game down to $48 for Prime members, saving $12 right off the bat. It was a good deal, because games don't tend to go on sale or get discounts for several months after release.