Q:

I miss the hidden right-click pop-down context menus like on Amiga Workbench. What happened to them?

Here is a question I've been trying to find an answer to for 20 years:
Why don't modern operating systems (e.g. MS-Windows, OS/X) still use the intuitive and space saving right-click 'pop-down' menu bars like their ancestors had (e.g. Amiga Workbench)?
The idea being that right-clicking (and holding) anywhere in the OS momentarily reveals a hidden context menu bar at the top of the screen. The menus and options available on this bar are context-sensitive, based on the object/app in focus at the time. 
This menu bar serves a dual purpose: it contains both context-specific menus as well as global system menus.
The result is a larger, cleaner productivity space, with control still available at your fingertips. 
Surely this is a better approach than the space consuming, always-visible application 'ribbon' bars and the various task bar/dock options plied upon us by most system vendors?
The closest I've seen to this in recent years are various Ubuntu builds.
Thoughts?

A:

I'm not familiar with the Amiga Workbench UI that you describe, and from what I understand the idea is that there's no menu that's visible at all times, and you need to right-click anywhere and hold, which makes the menu appear, and then while holding the mouse button down you need to operate the menu. This is a screenshot that I found. 

I can see a few issues with this concept.

Right-click has zero visibility. There is nothing to suggest to the user that she needs to right-click in order to display the actions. That's why Microsoft, for instance, has a rule that there should never be an action that's available only from the right-click menu. There should always be some other way of reaching that action even if it's hidden down several levels of other menus.
There is no current status indication. It's also a visibility problem but it's distinct from the previous one. With a visible menu, when you select an item, you can see which actions can be performed on it. Irrelevant actions disappear or become grayed out. That contributes to your learning of the system, your sense of control, and your general awareness of what's going on. With an invisible menu you need to take the first step towards performing an action (displaying the menu) before you can know whether it's enabled (until you've learned the system).
Difficulty of operation. It's physically much more difficult to operate a bunch of cascading menus while holding down a button, than it is without that constraint. 
Proximity of the menu. Today's right-click menus appear at the mouse cursor. This is literally the closest possible location of the menu to the cursor. If we replaced it with a top menu, it would mean that instead of having all your contextual actions within reach (a few  inches at the most), you may need to drag your mouse across the entire screen to reach any action. And that while holding the button down.

