[StavrosK]

Probably because reverse-engineering it is less effort than rewriting all the clients that Apple has already written.

[perryizgr8]

AFAIK Apple has written exactly 2 clients (Ios and Macos). It shouldn't be too hard to write 2 extra clients. In return you get to design your own open protocol from scratch and don't need to rely on Apple not breaking it at any point of time.