Physical releases are produced in batches based on what they think they can sell. If you find unopened bargain bin games, that's why. It isn't that they kept making it. It is that they made it and failed to sell it.

Supply and demand effects the used copies on Flohmarkt

As long as it sells I guess.

I remember still seeing some games for Win98 PCs in the mid to late 2000s EB Games and JB HiFi stores. They were dirt cheap, but still new I box.