To some NTs, feeling lonely can be a very powerful, sad emotion. One of the ways that loneliness manifests itself in NTs, I think, is that some NTs when they see a shy person or a person being alone, automatically assume the loner is lonely and sad, and then try to help the loner by forcing themselves into the loner's space, making small talk, or suggesting the loner immerse themselves in a bunch of people, which is how the NT would cure loneliness in her/hisself. So I think the disconnect is that the NT assumes the loner is lonely and then tries to help the loner the only way the NT knows how. But if the loner is an Aspie who is happy when alone, then this is where the NT would be wrong and could possibly be perceived as interfering, annoying, or pushing the Aspie into unwanted social situations.
This used to happen with me and my son, when I would see him sitting or playing alone and I would get an overwhelming feeling that he was lonely and sad, and I would try to give him a hug or somehow make him feel less lonely. Often, he would let me into his world and we would play together and this made me feel better, however I eventually came to learn that at these times he was not lonely and in fact was perfectly happy to be by himself. I also came to learn that there were times when my son needed or wanted attention, affection, company, or reassurance, and in those times he always found a way to get what he needed or wanted. So I stopped worrying about him being alone so much. But this took time and patience, and also an effort on my part to get to know my son better.
i_wanna_blue, its very difficult to say what motivates your relatives without more information, but hopefully at least this gives you one possibility to think about.