Why is there proprietary software in Ubuntu Software Center?

My question is very simple: how to get rid of proprietary software from the Ubuntu Software Center (USC)?

It doesn’t work to enable or disable repositories. Even with just the “universe” and “main” repositories active you can still see plenty of proprietary software. Examples include Skype, Slack, Spotiffy.

Tested: Ubuntu 18.04 and Ubuntu 16.04.

Edited: I had to edit this question down to exclude another bug that I previously reported here about how many open source apps in the USC are mislabeled as proprietary. Added that here https://askubuntu.com/questions/1052688/open-source-software-mislabeled-in-ubuntu-software-center-usc-as-proprietary

UPDATE: This question remains unanswered and I believe it is a very important topic so it needs more attention. If Ubuntu claims to be Free and Open Source then give me the freedom to remove the proprietary software from your official Software Center please. Newcomers to Ubuntu Operating System will not know how to avoid the proprietary apps from the Software Center, especially since when they (I, and all of us) install Ubuntu we may choose only the Open Source repositories, yet the Software Center is full of proprietary apps.

UPDATE 2: 33% of the software is proprietary when you visit the USC home. Video https://www.youtube.com/watch?v=PIVHQj7pfXQ&feature=youtu.be Also Krita appears as proprietary and I reported here Krita labeled as proprietary in Ubuntu Software Center

However the Software Center is full of proprietary software. How come? I thought Ubuntu is all about Open Source

Definition of "universe":

• Universe – Community-Maintained, Open-Source Software The vast majority of the software in the Ubuntu Software Center comes from the Universe repository. These packages are either automatically imported from the latest version of Debian or uploaded and maintained by the Ubuntu community.

  Canonical does not provide official support or updates for these packages.

• I would consider the tag "proprietary" a bug for chromium. It is FLOSS so should be tagged as such.

How to filter those out?

• I consider it a bug. If you do not want proprietary software do not include "restricted" (= proprietary drivers), or "multiverse" (= proprietary software).

• Do you have more examples of the tag proprietary in universe? Since I would believe it should not be in there.

• On how to filter out what is currently installed and is proprietary you can use:

  sudo apt install vrms
  

and you get a list of what is installed in your system

$ vrms
            Non-free packages installed on schijfwereld

amd64-microcode                     Processor microcode firmware for AMD CPUs
fonts-ubuntu                        sans-serif font set from Ubuntu
i965-va-driver                      VAAPI driver for Intel G45 & HD Graphics family
intel-microcode                     Processor microcode firmware for Intel CPUs

            Contrib packages installed on schijfwereld

iucode-tool                         Intel processor microcode tool

  4 non-free packages, 0.2% of 1852 installed packages.
  1 contrib packages, 0.1% of 1852 installed packages.
$ which chromium
/snap/bin/chromium

• Except for a font the others are microcode/hardware related so I good with that myself ;)
• I have chromium installed and it is not listed. Another bit of proof to believe is its a bug.

Bug report on debian (from June 2nd) that might be related: third_party/swiftshader/third_party/llvm-subzero/lib/Support/ConvertUTF.cpp in chromium seems to be proprietary. In the link there is mentioning of a fix.

There is a command called lintian to check DEB packages. It does not complain when I scan chromium 37.

The premise that Ubuntu is "all about open source" is not strictly correct.

The core of the OS uses primarily open source components, and Ubuntu developers support and contribute to a wide variety of open source projects.

However, Ubuntu has never required that all software in the Ubuntu repositories (deb) or Snap Store (snap) must be open source.

To filter for Open-source software, you could only enable Main (Officially Supported, Open-Source Software) As by this post already suggested you can edit your /etc/apt/sources.list and files in /etc/apt/sources.list.d/.

My other suggestion is installing an alternative to Ubuntu Software Center - App Grid. With this you can just about browse the open source softwares provided without some annoyances.

You can use a PPA file to install:

sudo add-apt-repository ppa:appgrid/stable
sudo apt-get update
sudo apt-get install appgrid