Why do people ignore me?

[Bob]

I have no friends. I only have like 4 actual good dependible friends that i can trust. And I try to make friends with other people. Say its on Facebook just trying to have a normal conversation with a girl. Ill say hey and it will say she saw it but no reply. And it happens 95% of the time with everyone. And also I sit by myself at lunch. I've tried sitting with other people. But they always ask me, who are you and how long are you staying. (I had to change lunches this new semester) But last semester i saw a kid sitting by himself so I asked him if he wanted to come sit with me and my friends. Why can't people just be generous and ask me that? Or say a simple hi? Or reply to a message? So my real question is, why do people ignore me?

I'm a 16 years old and am a Sophomore in high school.