I think that's less due to low intelligence or poor education it's just being completely out of their depth. I could probably do a car engine rebuild if I had perfect instructions that tell me EXACTLY what to do (and the right tools). But as soon as I got off track I'd be pretty clueless.

Don’t get started on UI updates to their most used programs.

If you've ever tried to read a foreign language book when your knowledge of the language is merely basic and tried to use a dictionary to solve the problem of many words being unknown, you'll know how frustrating that becomes and fast - one actually learns faster at the beginning by just keeping on reading even if not understanding a lot of things.

Further some of the "words" are often not words but acronyms, so not likely to be in a dictionary, plus a lot of domain specific words aren't in general dictionaries either (good luck finding the names of certain chemical chains and their properties in a general dictionary when trying to understand the booklet in a box of medicine).

Last but not least often even the explanations for some words require understanding of some concepts that people do not understand (most people probably know what "analgesic" is, but how many know what "antipyretic" - a not to far away concept given how many common medicines have both - is?).

Things which are supposed to be simple can turn into veritable dives down the rabbit hole to fully understand for those outside that expert domain if they were not simplified for ease of access to the general population, so it's hardly surprising if many people just chose to blindly use something as advised without even trying to understand it (which, let's be honest, it's probably the correct way for most people to used things like for example medicine if the source of the advice is a medical doctor).

Don't get me wrong: people should be more curious and more often trying and figure things out beyond the merely "how to use". At the same time, the information that comes with from expert domains in things targeted at non-experts should be as much as possible reduced to common language (though even that is a balance, since a ton of things required several layers of explanation to fully explain to non-experts).

That's a tiny minority of people and an ultra-specific belief.

I would say that the prevalence of the belief in fairy stories being real (aka Religions, Cults and so on) would be a pretty good indication of just how common and widely spread the Comprehension Handicapped are all over the World.

I think the modern flat earth idea started in the UK but I don't actually know of anyone who believes it, it's still very much a "village idiot" thing.