I think a large part of the move towards integrated head units had to do with the mandated rear backup camera that necessitates a decent sized screen in the dash in order to use it. The death of CD’s and CD changers also allowed for the screens to grow in size. Lastly, the touchscreens themselves are ever cheaper to manufacture. I love the giant screen in my Chevy Bolt - especially given the Google integration means I don’t have to use the nonsense baked in apps from Chevy.