1. Most Linux users know them. For Debian based distros [sudo apt install {appName}]. So simple.
2. Apps can be installed from executables like .deb and .rpm depending on your distro.
3. Flatpak and Snap are sandbox applications that can simplify the instalation process.
4. All of these have UI based app stores btw.

Also an OS isn't defined by how it installs applications

I already knew, no need to remind me

I can read it

All letters can be mathematic variables.