Not sure what Mazda's official stance on this is, but I think touchscreen doesn't work because it can be considered a safety hazard/distraction. Of course, one could also argue that fiddling with the control knobs is just as much of a distraction.
Personally, I find that it's easier to navigate through menus using the control knob vs. "hunting and pecking" at the screen. It's cumbersome at first, but once I got used to where everything is, it felt easier. For example, I can easily switch from FM radio to a bluetooth audio source and back without looking at the screen. With a touchscreen, I feel like I'd always be glancing at the screen to make sure I pressed the right button, even after memorizing where the buttons are.