So, you said you are not interested in friendship, which eliminates some disorders wherein people desire friendship greatly but are overwhelmed by the fear of rejection, abandonement, etc. Do you experience any anxiety or fears about actually building relationships beyond face value? Did you ever in the past feel fear or anxiety about building or maintaining relationships, but then evolved to avoidance, and then disinterest?

If none of those are you... I can think of one thing that it could be that isn't really caused by anxiety and fears, which is social anhedonia. It is where you have a decreased ability to feel pleasure from socialization, or interpersonal relationships. The characteristics of it vary between people. In general it causes decreased need in social contact, lack of friendship, and worse things as well, like depression... but it varies. To other peopld you would just appear indifferent about being friends with people. But it is because you do not feel a normal amount of pleasure and 'positive affect' from interpersonal relationships.