Because having each and every package on your system call to their own version of a package that already exists on the system somewhere else is bloated.
There is no reason for every application to have it's own packaged .so files all the damn time like what windows does.
Part the reason why most distros, even the shitter ones are faster then windows is because they don't run the same dependencies 50 thousend times.
And their not packaged in 80 thousend different places.
Even then, linux does have the option to do it in this way, only retards don't understand tarballs.
The reason why not every package does this, is because it's fucking retarded.
What you want, is a complete standard acrossed all platforms that use an already decentralised system of releases.
The problem is, you keep thinking of distros as a small part of linux. And you don't realise that the distro is "linux" As linux is, literally just a fucking kernel.
You don't fucking call every website "chrome" or "firefox" why the fuck do you do that for linux?
Distros, are not unlike the whole package of windows, because what distros are working with is PIECES of a system and they are PUTTING THOSE TOGETHER.
This means, guess fucking what? Different package management!!!!! HOLY SHIT!
Who'd guess?!?!
The person who made linux (the kernel) and the person who made bash are not related and don't have any real power over the actual packageing of the system, neither does windows if windows was released in a non proprietary standpoint.
Essentally, ever seen those windows operating system bundles? well it's like that, except instead of it being a product that is bundled together from the verius development sections at microsoft.
It's being bundled by randomfags online.
Like you have a section at microsoft dedicated to the kernel (NT) and then you have the section dedicated to the display manager are not in the same group, they communicate to eachother to make sure it's compatable but aside that they it's not their job to package it, that's the job of another department.
In opensource, we don't have this, everything and all the things are made completely transparent to the user, it's not a close box that's shipped out to everyone automatically on release.
This is what distros are for, to make sure these packages are delievered to you in a way that isn't fuckass stupid.
I know the windows comparison is very outreached as theres a lot of differences in how things work, but you really shouldn't be thinking of the system itself as one whole, rather it's all made out of tiny indivisual pieces that only recently started to make more since in the way it's structured and released.
This, if you really want to bash it. Is unix, because the idea is to make sure everything works together in a way that follows a rough standard rather, it's very friendly, just picky who it's friends are.
Distros try to fix small glemces of problems that arise from various packages in it's packagemanager, making it work well with others without completely having to redo any codebase.