Guy said he's not interested in getting to know anyone new. What might be a reason for that?

So there's this guy at my school that I have a crush on, he's in the same year as me, just a different class. When I see him in the hallway he always sits alone on his phone. People from his class told me that he doesn't really talk to anyone and he has nobody that he is closer with, he seems like he's shy or socially awkward. He also has no social media, doesn't talk to anyone from different classes either. Every time guys from his class invite him to their parties etc. he comes but just sits quietly. I have sent him hints that I'd like to get to know him since like April now. Once I came up to him at school for literally a moment, he seemed nervous and avoided eye contact. Recently I texted him and he replied that he's not interested in getting to know anyone new/he's not looking for a new friendship or anything like that. Of course I respect that but I'm wondering why? He has no friends at school, I think it's nice to have someone that cares about you and would like to talk to you from time to time, nobody says that we have to talk 24/7, just a quick hi, right? It's not that deep. We're 18, in high school, that's the best age to get to know new people. Why wouldn't he like to get to know someone new? Like what do you think might be a reason for that?