Tactile controls can become so thoroughly integrated in muscle memory that well-designed tools and machines (including cars) feel like an extension of thought. Think "volume up", it just happens automatically from thought to fingers to buttons.
Compare that to a multi-word speech command that requires perfect diction and phrasing over a span of five seconds. That's five seconds of distraction, longer if the command has to be repeated, vs milliseconds for the button.
Or he wouldn't be rated to fly the airplane.
In an airliner, the critical controls are all uniquely shaped, so the pilot knows by the feel which is which.
I think the most common commands can all be mapped to buttons on the steering wheel, which similarly is as close to possible as "negligible reduced driving capacity to use" without the tediousness of voice control.
But I do think the theoretical safety benefits of physical buttons that are not on the steering wheel as compared to touchscreens for features beyond the ones commonly used while driving are probably overstated.
And there's still room on the steering wheel for knobs for the most common controls, and voice control is often available.