[OkayPhysicist]

Once you're sticking a big ol' screen in the driver's vision during backup time, that screen becomes obvious real estate for any other user interface you may want. Buttons and dials are cheaper than a touch screen, but buttons and dials+a screen are more expensive than a touch screen.

[fho]

If I am not mistaken those touchscreens in cars are cheaper than the buttons they replaced (citation needed).

[AnimalMuppet]

Seems plausible, at least. A button is cheaper than a touchscreen, but you can replace N buttons with one touchscreen. (Citation still needed, though.)

[fho]

I guess at some point a (modal) GUI is more space efficient than individual controls.

At some point cars had screens, surrounded by physical buttons. I always thought that was a great compromise.