Context: I saw a post a while about Paradox Interactive cancelling their life simulation game Life By You and someone commented saying they wish Paradox Interactive would release what they've completed under an open source license. Follow up comments said it wasn't feasible largely due to a Russian nesting doll of licenses that wouldn't be compatible.

Question: What would be some obstacles in making a modern stereotypical AAA or indie game open source? Or even just segments for it for that matter?

This would be ignoring the financial impact. It would be like CD PROJEKT RED making Cyberpunk 2077 as open source as possible as a an action of good will.