At least for Gamestop, you're probably not wrong. Amazon Prime gets you new video games at 20% off MSRP. That's cheaper than what the distributor sells them for.
Go into your local Gamestop for a copy of Destiny 2 and see how hard they try to push you into buying a pre-owned (used) copy for $55 over the new copy for $60.
Their trade-in value for Destiny 2 is $24 (in store credit) and their pre-owned purchase price is $55. No wonder the sales staff force the pre-owned games over new.
Gamestop gave the middle finger to game producers when they realized how selling used games was way more profitable than new. When they file for chapter 11 in the near future they will claim downloadable games and competition from Amazon killed their business rather than their greed causing their suppliers to find alternative sales channels.
i'm on a slow connection so i can't find the links/news but i don't think that's true anymore. they certainly have restricted it. before it was including collectors editions. then it was only on preorders. not sure about it now but it's definitely not all just 20% discounted anymore.