They cost money, Donny.

I agree that MOST of what runs an arranger for day to day general playing be on buttons, etc., but most modern arrangers are WAY complicated. Putting most of the features that you MIGHT use (if you stretch beyond simple arranger operation) on hardware buttons and sliders would dramatically increase the cost, IMO.

Realtime operations on buttons, but editing and offline stuff on the touchscreen seems to be the best way to go about things, in my experience.