The counter-argument would be that game code includes valuable IP including frameworks, models, and so on, some of which might still be in use in other games.

The counter-argument would be that game code includes valuable IP including frameworks, models, and so on, some of which might still be in use in other games. Software is inherently fragile and dependent on surrounding technology. Buy a hammer, get a hammer. Buy (rent) software, you get something that only works on a specific combination of hardware and OS, perhaps only with certain libraries, packages, and other extras installed. So even with open code the game will still stop being supported on new platforms, probably quite quickly.