Linux is not an operating system or a platform, it's a kernel. Ubuntu, RHEL, Suse etc are operating systems, but more importantly they are separate independent operating systems. Their interoperability pretty much starts and ends with POSIX, everything else being more of a happy coincidence. And many of those major Linux-based OSs have strong vendor behind them.
Same way you don't expect cohesiveness between macOS and Windows, I think it is bit unreasonable to expect cohesiveness between RHEL and Ubuntu or whatever.
POSIX had a patch update 3 years ago, a minor update 12 years ago, and a major update 19 years ago.
That's the problem.
The desktop distros could and should have done a lot better to coordinate on fundamentals of user experience in the age of the open/hostile Internet and frequently updated software.
Unfortunately the website isn't loading for me. Wikipedia shows their projects seem to be focused on lower level graphics/UI issues, but not app packaging and security issues that have become very important in past 10 years.
Same way you don't expect cohesiveness between macOS and Windows, I think it is bit unreasonable to expect cohesiveness between RHEL and Ubuntu or whatever.