Inconsistent HUD with volume & brightness widget

I am currently on a demo license.
I have been playing around with the widgets, and I noticed that for volume & brightness sliders there is no visible HUD. After some looking around, I saw this thread (old) -

Now, when I drag the slider (volume or brightness) no HUD appears. Fair enough.
But if I tap the decrease and increase brightness buttons on the widget, the Apple HUD appears. This does not show if tapping the decrease or increase volume buttons.

So my question(s); is there a reason for the inconsistency? Can the volume & brightness HUD not be easily shown? And if not, then how come it is visible for tapping the buttons?

The volume and brightness HUDs would be a really nice feature, if it's possible.