I don't view games as needing to be open source as the end users doesn't need them to be productive in work. They aren't a part of a productivity pipeline and the discontinue of a game's support or radical change in fuction can't throw a person's livelihood into jeopardy.

Games should have a plan to release the source and assets if support ever gets dropped and I believe that it should be a requirement if a games gets to enjoy copyright protects that there's a plan for when it enters public domain, but that's a different discussion.