For example, distros don't provide the guarantees you're talking about - they arbitrarily introduce fragility (for example, by requiring shared dependencies that may have conflicting versions) and don't keep up to date with the upstream software that has bug fixes. That's precisely why software authors prefer to release as flatpaks - regardless what distro teams claim, bugs and crashes manifest as problems in the distributed software (not the OS) and are reported to the upstream authors whose users demand fixes.
In short, distros can't provide assurances that software will work. They can't fix it if it's broken, either.
I disagree that it isn't the software authors' job to distribute their software and fix bugs for their users when using it. The only folks who seem to insist that this is The Way Software Should Be Installed are distro authors and a tiny minority of users who are ok with broken code shipped by their OS authors instead of working code by the original authors.
Imagine if an app crashes on Windows or MacOS, a user reports the app crashed, and the author replies: "Sorry it's Microsoft/Apple's fault for shipping broken software on their end, complain to them instead." Because that's the same quality of user experience when a distro ships older versions of software or try and link against invalid dependency versions.