Why would installing one unity-scope remove ubuntu-desktop?

Solution 1:

Install aptitude if you don't have it installed:

sudo apt install aptitude

Then run:

aptitude why-not unity-scope-github

It will give you an output like:

i   unity            Depends   unity-scope-home  
i A unity-scope-home Conflicts unity-scope-github

So we can see that unity depends on unity-scope-home, and unity-scope-home is in conflict with unity-scope-github.

The other packages of yours also are a part of these dependencies, e.g: if you run:

apt-cache depends unity-tweak-tool

You will find out that it depends on unity .

And about the session-shortcuts, If you run:

apt-cache rdepends session-shortcuts

You will get:

session-shortcuts
Reverse Depends:
  unity
  unity

That means this package was installed by unity, and now that unity is going to be removed, you no longer need it.