Still I'm not so sure that UNIX (or programmers) is the source of it. I started with DOS (later Windows) and TP (later Delphi) so please don't think I'm biased here.
I have recently bought an Acer convertible for my mother with Windows 10 and so I'm getting a reality check on the sad state of computer usability in 2017. Teaching her to use an Android phone was difficult, but this is not better.
IMHO the reason of user-hostility is not some guild mindset, it's just that computer adoption is needed much faster than the time it would take to develop decent GUIs. The RTFM knee-jerk reaction comes later from people with some deep insecurities and not much imagination.
Totally agree on that UNIX is also a sort of walled garden. I'd say the same thing about GPL'd ecosystem, in this case for license issues.
If you can accredit Apple with one thing, it would be that they got this mainly right.
When it comes to Windows... I guess that's the result if one main player has a de facto monopoly over a certain software space. That, and "legacy reasons". It's like Adobe who couldn't even get their hotkeys merged between various of their big applications.