Unhackable Humans
People just can't see reason, and perhaps that's a good thing.
Nobody feels happy about it when explaining a stark, obvious fact, and hearing lazy, irrelevant nonsense as a reply. Telling people that X is a genocides, and all genocides are bad should make sense. Hearing 'yea-but', and 'whatabout' can make the blood boil. I don't have much consolation for this, except that this has to be the case, because the alternative might bring worse problems.
When I imagine what people can feel convinced by, though reasons, quite easily, a few things come to mind:
- Someone buying a kettle/ washing machine/ vacuum cleaner who doesn't know much about the device will listen to any reasons why brand X works better than Y.
- Listening to a historian explain why the Romans did something will always feel plausible, as long as the explanation doesn't immediately counteract anything else they know.
- Hearing expansions on old information - more on how bad people are bad ('that tracks'), good people are good ('that makes sense'), and that family member who's always up to something has been acting off, so maybe they're up to something ('sounds about right').
In all of these examples, the reasoning doesn't matter much. People listen to information and simply don't want to listen to anything which violates Logic or affects anything they care about significantly.
Salesmen
Despite salesman trying to reason people into things all day, despite their efforts at constructing seemingly-excellent reasons, their success rates remain low. People on the street who try to ask you to sign up for a charity, or insurance, or whatever, find perhaps a couple of people a day willing to speak with them. If the general public felt like making decisions based on syllogisms more often, they might end up buying a lot more insurance.
I don't think insurance makes a good purchase all the time, but in order to avoid buying insurance, someone either needs the reasoning skills to not feel bamboozled by armies of skilled salesmen, or they can reflexively say 'no', without any reasoning.
Mind Viruses
Bad ideas can spread quickly, but most of these bad ideas ('this brand of clothes is great', 'foreigners are bad', 'I need to get "beach-body ready" soon', 'the moon landing was a hoax') have very little impact on the person with the bad idea. If more substantial ideas could take hold, then people would either need such reasoning and knowledge that they could never be convinced by bad ideas, or dangerous ideas would spread as quickly as any lolcat meme.
With some tricky reasoning and false stats, entire countries might go to war overnight. Everyone could lose their money to a scam (as opposed to now, where only some tiny percentage of people buy into pyramid schemes).
So people don't think about reasons too much. They keep themselves safe from bad ideas by listening to everything, believing nothing of any value, and watching how other people, with other ideas, get along.
The Clothing of Reasoning
Still, to say 'I don't know why I do this, I just do', doesn't feel very nice. It sounds like you're an idiot. It's also not true that people don't reason about things - what I mean to say is that they don't reason much, and don't do things based on those reasons, but they will still reason a little.
I don't think I'll ever stop feeling annoyed by someone playing the game of 'I have good reasons for my beliefs', then pulling out transparent nonsense, but I understand the shrugs very well. Clearly Linux supports most users better than any other operating system, smoking should be allowed in pubs, and politicians need to do more about global warming very fast indeed. But if someone can only shrug at these ideas, and say 'I don't know about that', then I can't see anything wrong with that. It's not a matter of ignorance, but safety.
I do the same thing with most of my life. If you told me I should really eat less aubergine, or that I'd bought the wrong washing machine, I might shrug, and say 'really?', and I might even believe you. But I wouldn't do anything about it.