Some package managers do have differences that justify a separate project (nix, gentoo’s portage, etc).

For others, sometimes package managers are very similar feature-wise. But some developers would rather remake the thing because they would understand their code a lot better than someone else’s. Or because it would be far easier for them to customize rather than extend another project.

Imo it is developer laziness. Being able to use other people’s work is a valuable skill. But then again, this is open source, and people are free to develop the software they want the way they want.

“Are they….justified”?

1. Somebody thought the need for a new package manager was great enough to spend time creating one. That person at least must think it is justified.

2. We, the users, have not chosen just one of the options to be the standard. Does that “justify” that they all exist?

In the short term, the popularity of Linux is certainly hurt by the complexity of the ecosystem and the lack of standardization. As a product, it would see better adoption of it were more standardized. Without writing a book about why, there is no doubt about this. The short version is that, today, Linux is many products, none of which can compete as effectively as one would and all of them are impaired by the confusion this causes.

In the longer run though, it is almost certainly one of the great strengths of Linux. Linux is many products and as a result, it can target and effectively fill almost every niche. That is going to make it very hard for alternatives to compete at some point. Once Linux knowledge and Linux applications ( yes, I know ) become more mainstream, this compatibility between options becomes a strength. I can have my own operating system that is just the way I want it, but it still runs Docker and Stream ( as examples ).

Think of the cereal aisle at the grocery store. If I want to introduce a new cereal ( or pasta sauce or whatever ), coming up with one that has 10 flavours is not going to work ( without immense marketing muscle ). None of them will sell well enough and probably all of them will get pulled from store shelves. I would be better off launching one. However, once I have a mature market position, I can have not just the regular version but the whole wheat version, the honey nut version, the cinnamon version, the holiday version , etc. They will collectively make each other stronger and all potentially sell well ( again, think pasta sauce flavours if that makes more sense to you ).

This is why there was The Tesla Roadster at first and now there are the Model S, Model 3, Model X, Model Y, and maybe the Cyber Truck.

Linux is not a “product” though. It is an Open Source program. While any given Linux distributor ( distribution ) may think like I outline above, collectively the Linux market is fragmented. Linux is a mix of commercial, community, and individual interests all scratching their own itch.

I am super interested in Chimera Linux right now and fairly negative towards Ubuntu. This makes me part of your problem though. Chimera Linux makes “Linux” less predictable, more confusing, and more frustrating for new and potential users. Pushing everybody to Ubuntu would be a better market strategy. That said, I personally want to use Chimera Linux and, while I say that I want Linux to succeed, I also secretly hope that Ubuntu will fail. Chimera Linux uses a package manager used by only one other Linux ( and in fact they use different, incompatible versions of it so really they are unique ). Clearly, my priorities are mid-aligned with the premise of your question.

So, what does “justified” mean in the Linux space.

Imagine having only one option, and that option is dnf. I’m out. I don’t want Linux anymore.

Convenience/ease of use; There’s a little caveat that only “true linux users” are able to notice, tho –

… compiling is, and always will be, the best option.

I wouldn’t worry too much about the package manager, just worry about whether the distro has a good package repository. If it has all the software you want to use, then use it. In my opinion, most package managers (dnf, apt, pacman, xbmp) are basically the same, and you would only notice a big difference if you ever tried to make your own package for your own software.

That said, a few package managers are very different from all the rest:

• Crux OS “prt-get”: simple and stupid: just downloads and installs tar archives.
• Gentoo “emerge”: builds all software from source code when you install it. This provides some guarantees that the source code was not tampered with by the distro maintainers, this is great if you need to review all of the source code that is running on your system, but terrible for most people who don’t want to spend so much computing power on compiling stuff every time you do a software update.
• Nix and Guix: creates its own blockchain-like database of isolated package dependency chains on your system, allowing you to instantly roll-back to the previous set of installed packages if you ever install something that breaks your system. It also guarantees that the software can be checked bit-for-bit (using SHA hash) traced back to the exact version and dependencies of the source code that built it. Nix and Guix packages also live peacefully side-by-side with any other package manager since all Nix/Guix apps are completely self-contained within its own database. In a way, it is sort of like one big AppImage or Docker container, but you can just keep adding or removing stuff to it as often as you want.
• Silverblue, SteamOS, VanillaOS, BlendOS, CarbonOS: distributes “immutable images,” so it is impossible modify the operating system at all. Updates will ship an entirely new operating system with all packages built-in. However you are allowed to install software into your home directory, and you can install FlatPacks and AppImages. This provides a great deal of security in exchange for a tiny bit of inconvenience.

My personal preference: I use ordinary Debian or Ubuntu to install the critical software that needs to be stable and reliable, and I use Guix OS on the side to install the bleeding-edge things that might break a lot.