Assume you got source for a game written in a proprietary game engine. If you don't have access to the game engine itself, nor the API documentation, etc, how long will it take to get this game running in your manner of choosing?
The infrastructure in these companies is a huge amount of scaffolding that's non-trivial to replicate.
The infrastructure in these companies is a huge amount of scaffolding that's non-trivial to replicate.