I have no clue guys. That is just the number I remember people talking about years ago.
Edit: As for the games going cheaper after launch or 50% within a few months (cough cough Ubisoft), the vendor subsidizes these discounts. Obviously Walmart, Gamestop, Amazon, etc. are not eating a loss. The retailers will get a discount for selling them cheaper. This is why you will see Gamestop, Amazon, and Best Buy all have the same discount on certain games at the same time. Immortals: Fenyx Rising for example is consistently on sale for $30 (50% off).
As for "why not just keep the game expensive and never show the real clearance price so they can send it back and get credit?" Well, what do you think is going to happen when the vendor finds out they do that or that they aren't promoting/pushing their games or showcasing them on the floor? Or what is going to happen when Gamestop sells a ton of Game X but Walmart sells 1/10 of Gamestop's amount? Walmart is going to lose their bargaining power or be given less copies that would normally sell a lot of.
Also, if they can't send certain games back for "X" amount of years, it is better to get it sold at a cheaper price than to have it sit in inventory or take up shelf space than to hold it for 5 extra years.
Now that last point doesn't make sense for the recent PS4, X1, and Switch games as many of them were only 1-2 years old...so no clue why they got recalled so early. Untitled Goose Game for example has only been out 6-7 months. But that point made sense in 2018 when we were buying up Rhythm Heaven Fever, Metroid Other M, and Dragon IX. Those were all 5+ year old games taking up shelf space that no one ever bought. And when I say no one ever bought, again this is on a store to store basis previously. This most recent recall seems to be much more widespread.