They're not. I'm using them as an example of the "bad" in Open Source development.
But it's also not so much the individual OS components that are a problem, their interactions are just as fragile and usually subject to neither party taking ownership of the problem.
We forget that it this organic nature that makes open source what it is. Nobody charges you entry fee, there are no hidden fees once you enter, nobody is trying to sell you crap but you need to learn how to survive yourself. Once you do that, you understand how to deal with shortcomings of a package or finding another solution to your needs. Sure it takes time, but when that becomes second nature and you stop fighting the nature of the ecology itself, there is no other system like it.
That's why comparing it with advantages of other systems is pointless. I didn't choose to walk into the forest because it was a perfectly tailored experience, I did because I wanted freedom. It required me to learn how to fit in and now that I have, I'm at peace with where I am.
Gnome have been chopping off their own limbs because it reduces weight. All in the name of simplicity. I think they are not the best example of Open Source development.
KDE on the other hand had a hard fall once and basically recovered and invested long term in Plasma and that has paid off handsomely. Today, it is one desktop that I can say is closest to typical/standard desktop paradigms out of the box while retaining a high degree of flexibility for those who choose to customise it. I have been using KDE on Fedora for a while now and it has been basically solid.