I think this is really insightful. A lot of wisdom here, I hadn't thought of it this way, but this is me too. I don't like attention on me, I couldn't tell you why. Have you figured out why?
Haha, well, that' tough to answer. It's like giving a doctor a symptom and asking him what could be the cause.
I personally think it can be divided into one, or all, of three groups:
Whether we want to admit it or not, most of us are insecure over things. We, as a people, misunderstand where to find our worth, and so we start to find our worth in areas where we shouldn't--money, materials, relationships, so on. This can make us feel insecure to other people, and when the focus is on us, we fear those insecurities will come to light, and people will be able to clearly see them. That prospect is uncomfortable. (I feel more shy types fall into this category.)
Complicated to describe this section, but a feeling if disconnectedness comes from awareness. We see people, and we watch them interact, and to our eyes, it comes off like a game. A social game. A game they are unaware they are playing. But because we are so exquisitely aware of it, we feel a little disconnected from forming relationships with people. When someone asks us a question about who we are, or our past, we feel uncomfortable. We know they're asking because it's simply what you do in that situation, like when you go to the doctor's office, and they ask you what you did for the holiday. It's not that they're incredibly interested, or will remember after you leave--it's just something you do. This awareness is awkward to be aware of, because suddenly interactions feel disingenuous, despite the fact that those people are unaware that everyone does it. Thus, having focus placed on us isn't great. We crave more genuine conversation, and knowing that you're about to share parts of yourself that isn't going to be remembered, or isn't really wanted by the person, makes us not want to do it. So, we focus on the other person.
Think of it like coding in a video game. The coding is the final reality, but the game itself is also a reality. And while most people are in the game, others see the code. Once you see the code, it's hard to behave normally in the game. A question about your interests isn't just a question anymore, but numbers. (I find more intuitive people fall into this category. Those too lost in their own head.)
Vulnerability is painful. Being able to be open to people, and freely share yourself, is a risk. You don't know if they're going to judge you secretly, or if they're going to dislike you. If you're someone who lives your life as a peacemaker, like 9s, for instance, where you've carved yourself into a state of neutrality, opening up about anything leads to a lack of neutrality. Think of counselors. Their job is to constantly focus on you, and ask you questions. They have empathy, but they aren't vulnerable. The moment you ask them a question, they're thrown off guard. There's entire courses in grad school for counselors to be prepared for when a client turns the tables. An you don't need to be a counselor to be a counselor type. When you spend you whole life helping others through their problems, and no one ever asking how you're doing, it can feel uncomfortable to experience it. Like a superhero who is never the one being saved. (I find Fe types to fall into this category).
And a trait all of them share is habit. The more someone doesn't ask you a question, the more you don't have an answer, the more troublesome it is for someone to ask it. It's a cycle.
Say you're studying something in school, like psychology. You love psychology. It's just something that interests you.
Finally, someone asks what you're studying, and you answer. And then they ask a question you weren't prepared for: why do you like studying psychology?
You kind of freeze, and stumble through the answer. It's not that you don't have one, it's just that you never prepared one, because no one's ever asked. You haven't filtered through what you what to share. You haven't made sure it either hides your insecurity, feels connected, or isn't too vulnerable. You lose the control. And you hate every moment of it. Kind of like stage fright. So you avoid it.
"...I just like learning about why people do what they do. But, anyway, what about you? What did you study? What got you into it? Oh, that's cool, so what kind of plans do you have?"
You go back into comfort mode, and focus on the other person, avoiding the training it requires to open yourself to others. Because it does require training. However, "most" people like talking about themselves (which is why a quick way to make someone like you is by asking questions), so most people get the training needed. When you lack it early on, it creates a habit.