I doubt if it's actually cheap. "The touchscreen" aka 2DIN radio/infotainment head unit slot, is required for Japanese market, as Japanese users require one of indigenous options installed for all cars. Google Maps supposedly had gotten better but aren't quite replacing it, so CP/AA doesn't work. I believe this is a unique country requirement, as many Chinese EVs as well as many European low-end cars seem to ignore it.

Not every cars are made for Japanese, far from it, but abolition of LCD based map-radio on a standardized slot is a weird hill to die on, so every cars has it anyway.

And, I think, this is where the actual "it's cheaper to..." argument begins: since every cars will have the standard issue map-radio, it _can be cheaper to move buttons into it_. Differences between the standard version and one with this context is whether the cost of the entire 2DIN screen is included in it or not - if the screen cannot be removed, to shut up whining Japanese or not, it becomes sunk cost and becomes a constant term of equation, which physical buttons have no chance of winning.