One of them main reasons for that, I think, is how the average non-tech computer user perceives UI/UX, when they have been exposed to only a single type of interface for most of their lives (most probably Windows).
And even though they tend to pick up different UIs in mobile phones fairly quickly, that seems to not be the case for computers.
Back that up with earlier versions of middle-school computers studies in being mostly like:
How to print a file in Microsoft Word?
How to copy a file to USB drive? (with the implicit - using Explorer on Windows XP)
And you have most of the population thinking that's the only way to do it. That was the case with me until I learned programming.