This is not applicable to games.

Bose's brand is built on audio quality. There is close to little negative impact open sourcing the API (server) in this case will bring to their brand.

For a game, open sourcing the server generally means anyone can basically mess it up and with the internet make it available to everyone to see. Then the responsibility is on the developer to protect their "brand".

The plethora of WoW private servers is not a good example. These are from individuals, or groups of people who willfully reverse engineered it on their own. This is different from a company expressly permissing and implicitly giving a grant on allowing a similar product to exist - the difference is that one gives credibility, which the other does not.