> 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

Because why give something out for free when you can offer that stuff only in the most expensive models?

If you look at http://www.gphoto.org/proj/libgphoto2/support.php http://digicamcontrol.com/cameras its almost universally older stuff and hiend models. At some point they stopped exposing control in order to upsell.