Even the 1980s car radios with digital controls had no perceptible delay, despite containing microcontrollers with a tiny fraction of the speed and memory of the modern ones.

Maybe it's the whole "let's run Linux on it because we can" phenomenon. The microcontrollers in the old electronic radios didn't run an OS but interacted with the hardware directly. The number of instructions executed from sensing the dial change to updating the tuner and display would probably be less than 100. Now it's half a dozen layers of abstraction and millions of instructions to do the same thing, on a processor which is maybe "only" 1000x faster at most...