I think I have found the answer to my question about meetups – or, more specifically, about why we have them.
It is because spending time with other asexual people is the closest to our home planet as we can get.
I have written before that I feel that I must be from another planet, and it appears that some other asexual people feel the same. In fact, I have felt that way all my life, not only because of my orientations – since I was not always aware of them – but because I could feel I was different from other people I knew (especially people my age) in various ways: I did not have the same interests, use the same slang, care about the same things. Because of that, I found it very difficult to relate to my classmates; it seemed to me that we could not be from the same world at all. Now, of course, it is because I am asexual and aromantic (and aware of those orientations) that I often find it difficult to relate to others – and in a way, it is maybe worse than when I was growing up, because back then I still could relate to my family and feel that they, at least, were from the same planet as I. But it is not the case anymore; my parents are very understanding of my asexuality and my aromanticism, but still, they are not asexual or aromantic, and even though they try very hard to see things from my point of view, and succeed most of the time, that does not make them asexual or aromantic. They try to understand how I feel about things, but of course they do not feel the same. When I am with them, I feel I am in a safe place, among friendly natives – but they are not from my home planet.
Until very recently, I did not think I actually needed to be among my own kind. I have never really minded being alone (this is actually my natural state of being; I am always glad to spend time with my friends, but I do not need other people around to be happy), so feeling I was from another planet did not mean that I felt isolated on this one. I daydream sometimes about what my metaphorical home planet would be like, but I do not long for it. Or so I thought.