I am just totally guessing here but may be this is because Samyang, like most 3rd party manufactures have to reverse engineer their product to fit, somewhere along the line, there is a bit of the information missing.
i.e. If for a Sony lens to focus with a Sony camera, there must be say….picking a number out of thin air here, say 10 elements that have to align for the camera to say "Yup, its now in focus". It's almost like NASA launch going. Fuel - Go ! Life Support - Go! Ignition Go ! etc etc etc.
Perhaps Samyang have figured out 9 out of the 10 things that the camera checking but not 1 or 2 things, minor things. In return, the lens will still work but it's still missing something, some code or some check that it doesn't talk to the body about.
