> I am an amateur photographer, and I can't understand why the major camera brands (Canon, Nikon, Sony, Fuji, etc.) aren't open at least to the concept of SDK's to control their cameras (let alone opening the lens mount specifications)...

I don't know about the other brands but Nikon cameras have implemented PTP in full forever which allows you to set virtually every option remotely, albeit over USB. I'm assuming the other brands are similar, because that's how tethered shooting works. There is no camera-specific SDK or driver needed for this. The bluetooth and Wifi stuff is proprietary ad vendor-specific as far as I know, though.