If you consider something that does not work reliably to work, you're right. I don't.
A distribution has to consider more applications and use cases, but it also has more resources. Doing things at the distribution level is much more efficient than each user doing their own thing, that's why they exist.
You’d expect (hope) core applications would be tested but what about stuff that’s not in the official repos? Or stuff that is but had a new feature unbeknown to the distro maintainers?
On HN last week there was a GUI bug in a core OSX utility being discussed that slipped through Apples testing. If they managed to overlook something in their own OS, then a smaller team of people, likely working for free in their spare time (remember a lot of the distros that ship non-standard themes as a default are spin offs) is unlikely to test every GUI form and dialog that can be rendered o. Linux.
End users can make that choice with regard to the extremely limited set of applications and use-cases that matter to them. A distribution has a far wider landscape to consider.