I always assumed it was because, when you make an interface&#x2F;API public (by documenting it and offering it to your customers) you have a professional obligation to keep it reasonably stable. People get understandably upset when APIs for things like twitter and facebook keep changing under them, making things that worked before stop working.<p>Making the bitstream format a public API would make it harder for them to change&#x2F;update&#x2F;improve it without making themselves look like assholes for breaking third party software.