Your car HUD doesn't do this.
I hear you, but I can tell you that the car HUD does
not require refocusing - it is absolutely clear and crisp at infinity requiring no adjustment that I can notice. (I have experience on HUD developments dating back to the 80's). I believe it is fixed at infinity, perhaps?
Of course, I don't have a head mounted display, so its only valid for the direct frontal view.!