Why would she ghost/ignore me?

Recently a girl that was in my childhood class for 6 years popped up in my instagram suggested. I remember we used to have a good relationship, we were good friends and I used to have a crush on her. But this was long ago, I'm way past that.

So when I saw her on my suggested on Instagram, I sent her a follow request and messaged her " Long time no see, how've you been? " but got no reply. I was just being friendly, and thought it would be a cool thing to do.

Any ideas on why she's ignoring me?
Why would she ghost/ignore me?
Post Opinion