Perhaps ironically, this is mocking a strawman. Flatpacks can be installed and managed using the terminal! Not only that but Linux-Distros have had graphical package managers for decades.

The primary reason that distros have embraced flatpack / snap / appimage is that they promise to lower the burden of managing software repositories. The primary reason that some users are mad is that these often don't provide a good experience:

• they are often slower to install/start/run
• they have trouble integrating with the rest of the system (ignoring gtk/qt themes for example)
• they take a lot more space and bandwidth

Theoretically they are also more secure... But reality of that has also been questioned. Fine grained permissions are nice, but bundling libraries makes it hard to know what outdated libraries are running on the systems.