Turn the physical volume dial on a car with a slow Apple CarPlay interface and tell me how that works out for you.
Oh, it's too loud? But it takes 2 seconds for the software to respond due to lag and now you're fiddling with the volume button trying to not make it worse?
A physical button didn't fix that.
If it worked, great; if not, oh well; no need to look at it and try again though. That's the benefit.
My Android phone has a similar issue while operating over Bluetooth. While holding "volume up", it takes several seconds for the volume change to register. So I have no feedback for how long I need to hold "volume up". If I wait until the volume is loud enough -- it keeps going up for another two seconds, to the point that it is painful and possibly damaging my hearing.
Rapid feedback is important.
When using a touch screen, if you don't know whether the lack of feedback is due to its lag or your bad aim, you would likely take your eyes off the road in order to aim better, given that bad aim is a likely culprit.
I know the one it was on, and I know how far to turn it to get to the one I want. This removes the necessity of looking at it.
Same for steering wheel buttons (e.g. Up - next track, down - previous track, same for volume)
Same for wipers - only 3 positions and you can tell by their speed which position it's in.
The problem is when manufacturers take existing solved problems and move it to a strictly worse system like touchscreen. That's an inexcusable regression.
If it doesn't change -> change it more
It it changes too much -> change it less
If you realise it needs to be moved slowly -> move it slowly
The car when started always turns on the radio at the last volume the radio was on at, regardless of whether it was on when the car was turned off.
More than once, I have turned it on, and it was playing at full volume the Sirius FM ads, and would not lower the volume or turn off ( via the other physical buttons) for at least half a minute. I've done some damage to the volume button after that, and I have taken to just getting out of the car until the stereo responds.
The default on the car is to turn on the radio on engine start. No way to change it. No way to make it remember that the last time the car was used it was set to Bluetooth audio. Switching back to Bluetooth requires navigating through 3-4 layers of menus. Even when you turn it off, it randomly turns back on for no reason. :/
My 10+ year old VW: remembers which audio source was last used. Phone autoconnects via Bluetooth every time with no hassle. Volume is never an issue (real buttons that respond in a timely manner on the steering wheel). Off is off until you turn it on again (with a physical button).
I know where the volume knob is and I can easily grab it and turn it without looking away. If it's slow to respond I can go again and dial it back down, without looking away. Or I can just keep my hand on the dial and spin it back a bit.
With a digital screen I can't leave my hand on it without continually pressing the input, and if I want to put the volume down I have to look and see where that button is.
A physical control absolutely fixes this