There’re are some difference between a codec or OS with a game engine. One is the user base. I think there’re simply not enough game developers to extensively use the open source engines, every single computer needs an OS and in most cases needs a codec. But not everyone is a game developer. Another one is requirements I guess. For OS and codecs, I think the requirements are much more defined and manageable, but for a game engine the user uses it to create something else, hence the capabilities needed from the game engine may change wildly per project.