In my experience, regarding the "how was your day?" question, it's usually just the opposite. NTs tend to say things like "how was your day?" without really wanting a detailed explanation but more because they want you to ask about them/theirs. So the expected 'answer' tends to be, "My day was okay. What about yours?" Hence, going into much detail about the events of my day tends to be a conversation ender.

I can't speak for all aspies, but there are two reasons I tend to give short, non-committal answers. First and foremost, a question like "how was your day?" is actually, to me, a lot more complicated than it seems. Specifically, it's vague. It could simply be a canned question with the expected answer being a canned response, e.g. "fine". It could be an intended segue to a follow-up question, as I stated above, and therefore really mean "ask me how my day was". Or it could signify genuine interest in the events of my day and my reactions, primarily my thoughts and emotions, regarding said events. In the latter case, I may not have any emotions toward the events of the day, or I may still be processing them and not know what those emotions are just yet and, therefore, be unable to talk about them. I'm alexithymic, meaning my emotions are blunted, and it takes time for me to process them. The best way I can describe this is, I don't readily feel happiness or sadness or disappointment or love; I fell pressure, just an internal pressure that could be any number of emotions, or could be general anxiety, or could be from eating too many tacos. So I may actually not be able to answer the question, and so will just say "fine" or "okay".
So, in two of the three scenarios, "fine" is the best answer, or the best one I am capable of giving. That's two of the three scenarios; not two out of three cases. The first scenario is by far the most common, meaning that "fine" is, in the majority of cases, the 'correct' answer.

And that brings me to the second reason. Early in life, I commonly said/did the wrong thing(s) in social situations. Without any real context as to what is the right thing to say/do, or why that is the right thing and another is wrong, social interactions became trial and error, with each success and failure adding to the ever growing lists of 'what to do' and 'what not to do', respectively. Consider the following dialogue:

A: "How was your day?"
B: [Goes into long explanation of the day's events and B's thoughts and feeling of said events]
A: [interrupting B] "wow, you could have just said 'fine'."

Having this happen only a few times--or maybe just once depending on the ramifications of the conversation (as in A never talks to B again. Yes, this has happened to me.)--is enough for that response to go onto the 'what not to do' list.

So, both logic and experience tell me that 'fine' is by far the safest response. It's not that I don't want to talk about my day or don't want to hear about yours; I need more, however, than "how was your day?" to indicate that a deeper discussion is wanted or even welcome.

I see your point. I do. And I do agree that we have to learn to live the world according to existing rules and expectations… to an extent. It goes without saying that one should obey traffic rules if one is to drive a motor vehicle, and similarly, one should learn the rules of social engagement, e.g. manners, respect, etiquette. But it is rather unfair to expect us to change completely to fit into a society that refuses to change or allow any leeway for atypical behavior, and for the very same reasons that it would be unfair for society to make no allowances for other disabilities.

You see, our brains are different… physically different. You can see ASD on an MRI. It's truly not a matter of being stubborn or unwilling or just not getting it; it's a matter of a brain that works differently, that processes stimuli via the 'reasoning' prefrontal cortex versus the 'reactive' amygdala. (This is not to say that nerotypicals don't use the prefrontal cortex.) The amygdala the in ASD brain is smaller and less active with fewer neural connections to other parts of the brain, meaning we are less aware of not only emotional cues in the environment, but also of our own emotional response to stimuli.

Expecting a person on the spectrum to fully grasp the nuances of eye contact, body language, and the like, to process and be able to talk about their emotions in the same way and on the same level as an allistic, to interact with the world primarily through emotions rather than primarily through reason, is the same as expecting a paraplegic to get out of their wheelchair and dance. With some treatments and with grueling physical therapy, some people are able to gain/regain some mobility, but those cases are rare, and rarer still the case of complete mobility.

Likewise, some aspies are able to 'pass' or act mostly neurotypical, but it is only ever an act and always a struggle. Furthermore, this is a catch 22 type situation. We can be comfortable with ourselves and accept our oddities-- stim in public, rock back and forth and talk to ourselves, say what we are thinking no matter how socially inappropriate or irrelevant to the topic or situation-- and of course be shunned for it. Or we can put extreme effort and energy into learning how to act 'normal', hide who and what we are, disguise ourselves. We will probably be accepted socially, at least in public and on a superficial level. Of course, we still will have trouble forging deeper connections, and if we do manage to make friends we may not be able to drop the act around them, otherwise they might feel blindsided and maybe even resentful that they were not fairly warned about what kind of relationships they were getting into.

And as for the whole 'this is the way the world works' argument, well, what about your phone, PC, tablet? The internet? The programming that runs them all? Modern math, physics, systems of governance, music, economies? Newton, Einstein, Thomas Jefferson, Leonardo DaVinci, Galileo, Alan Turing, Michelangelo, Charles Darwin, Mozart, Beethoven, Adam Smith, James Joyce, Jonathan Swift, HD Thoreau, Immanuel Kant, Bertrand Russell, Socrates, Bill Gates, Charles Babbage, Warren Buffett, Archimedes, Pythagoras, Stanley Kubrick… the list of historical and living geniuses with confirmed or high likelihood of ASD is enormous, and their contributions even larger.

Try to imagine how different the world would look today without these people. Should the world change for us? Maybe not. On the other hand, maybe it should, however, at least accept that we are not a small group of autists struggling along in an allistic world, but rather that we live in an autistic world that just happens to be populated mostly with allistic people. Why then do you get to be the arbiters of culture? Why is your way right and ours wrong? Because you outnumber us? Do I need to point out that insects outnumber humans?

I say this to elicit some deeper thought on the subject, not to offend. And please don't be offended. I find your posts honest and insightful.