The simple reason is while the images are beautiful, there are 3 main reasons.
1. I want to take pictures 'away from the car', ie, you can-not take camping equipment with the Seitz equipment as it is just too heavy and bulky.
2. At 52 my knees seem to be getting 'dodgy' ie I can start feeling them getting painful if I carry really heavy weights, especially up hill. (Weakest link in the chain as it were!).
3. I am getting more into workshops where Nikons etc are more suitable or relevant.
So when I look at the overall picture, I can find a smaller lighter camera, save my knees and not really loose any market in terms of print sales. Indeed the change would free me from the restriction of having just a 90mm and 250mm lens and allow me to shoot in more remote locations with a greater lens choice.
According to Schneider the lens covers 110 degrees at F22 and 96 degrees at F5.6.
I know Seitz state you can use a 75mm lens, but I have not tried.