I’ve given you quite a few reasons, you just don’t care.
Let me put this really simply. Canonical fucks shit up with their patches. Users experience this as buggy software. Users file bug reports to the software. The bugs aren’t valid because the problem is with Canonical’s mess of patches. That is bad for me as the dev, because I have to triage that bug and determine that it’s Ubuntu, not my software. That is bad for you as the user, because software that works perfectly fine on any other system doesn’t work on yours. This is also bad for you because the devs that build the software you use have to waste their time tracking down Ubuntu bugs, instead of spending their time improving the software you use.
Maybe you don’t consider this a problem, because you’re used to how buggy Ubuntu is, or maybe you don’t use any software that Ubuntu has fucked up, but that is a problem that people experience, and if you don’t see that, that’s a you problem.
Also, I specifically didn’t mention “what I prefer”, because it doesn’t matter. Canonical is the only big Linux company that does this to an extent that devs waste their time on it. Any other big name distro is better than Ubuntu.