Unlike Tsubaki, who's mostly friendless due to severe social anxiety issues and visibly suffers from it, Hiiragi gives the impression of being solitary out of preference and mostly plain uninterested in socialising with people
I know from lived experience that some people mask their social anxiety with the appearance of disinterest
Sure, but so far we've seen Hiiragi has no problems interacting with people when she wants to - that's just really rare.
The reasons for her aloofness rapidly turned out to be pretty grim tho... :/
It’s not one shoe fits all. Take me for example. I don’t have friends who I can talk to because of social anxiety dating all the way back to my youth (aside from like family friends - basically family). However, if I get comfortable around people, I can’t shut up. And in recent years, I’ve gotten better with interacting with strangers. Although, I’m comfortable by myself, I’m still working on socializing more with others.