It's the fault of 'the inmates running the asylum' thinking that visual gimmicks + removing functionality until the product is lobotomized == User Experience
And don't give me the BS that Gnome cares about UX, they don't.
How do you know you care about the user? They like you. Sometimes they even like you enough to give you money.
[and I have exactly the feeling you do: it gets out of my way except when I want to use it, and then it's easily available]
The gnome shell especially is also a welcome sign that there's some independent thinking about UIs going on, which is a welcome change from the painful old "let's be just like windows with a few tweaks!" schtick of times past.
Its worst sin is that it represents change, and, well, people hate change... :[
I don't know why I'm bothering to respond to such a ridiculous and unsubstantiable claim, but there's actual evidence in the form of work product that GNOME cares about UX. It can be found here https://live.gnome.org/Design/Contribute
But this is not evidence they know what they're doing. Or the designers may know what has to be done, but the organization doesn't know where to go. Maybe it's committee driven design.
They may talk about it, but it's like a presidential campaign speech: "Yes, we care about education, about healthcare, etc" but it's not necessarily true.
Their designers are good, and some good things come across, but in the end it's like having a car with a powerful engine and a crappy suspension, and it's this that shows in Gnome, they don't know how to put together a nice car, it always ends up with a ridiculous aerodynamic, small tires, etc