Yes. Firstly because no distro has everything in their respositores, and secondly because different package managers serve different purposes.
The closest to an all-encompassing package manager is perhaps Arch with AUR, though you are forced to use tools beyond pacman if you want actual package management for the AUR packages. AUR has also shown itself to be a massive liability, since the only way the project has been able to cover as much software as it does, is by doing next to no vetting of the submitted packages. With predictable results
If you used the GUI app you probably wouldn’t see that your system uses different package standards
The GUI that came with my distro only covers 2 of the 4 package managers I mentioned. And I’d have to use a GUI
Is there a good reason to use more package managers? When I need packages that aren’t provided by the distro I’m using, I change distro
Yes. Firstly because no distro has everything in their respositores, and secondly because different package managers serve different purposes.
The closest to an all-encompassing package manager is perhaps Arch with AUR, though you are forced to use tools beyond pacman if you want actual package management for the AUR packages. AUR has also shown itself to be a massive liability, since the only way the project has been able to cover as much software as it does, is by doing next to no vetting of the submitted packages. With predictable results