Well, maybe because digital is better at showing small differences in this case? Like on a 50kmh road, dropping below 50 is quite noticeable in digital, less so with a line above or below another line.

But for the revs, I think it's quite clear that the analog is better.

Maybe one way to put it would be how important an exact value is? For the speed, it is. For revs, the relative value and its change is much more important and humans track movement much better.