Linux is super fragmented (and generally has been historically).
If more people in Linux agreed to develop, use, and support the same distro–similarly to how most of us use the same kernel–then that distro would probably be better than Windows and more people would move to Linux.
I get what you mean from a development perspective, but I already know your opinion is and will expectedly be unpopular within the Linux community. People here like freedom and choice, in one way or other.
A big benefit is that it keeps threat actors away from most components. If there’s a vulnerability in some Qt library, it will be big enough that people will notice eventually and fix it, but too small for someone to write ransomware code if the target is like 15000 random unimportant people.
There are certain things that people are trying to improve upon, to make things uniform/easy like the many ways to install software! Package managers to avoid having to compile from source. Flatpak/Snap/etc. to avoid having to deal with packages and dependencies! AppImages to put everything in one portable binary! However, with increasing simplicity you trade off customizability and other factors. This is why all these ways are available.