Why wont he follow me back?

[I Should Be Sleeping]

I met a guy a few years ago through a friend, really cool guy. I recently stumbled upon his account on Instagram and followed him, but he wont follow me back! I'm just wondering why somebody wouldn't? I don't post excessively, or even often, and we have a similar sense of style and taste in music. I thought hey he's cool so I'll follow him, maybe he'll follow back.
Any ideas on why he wouldn't? It's really not that important but I'm just curious because things like this bewilder me and I thought he'd be an interesting friend. I bet if it was Facebook he would have accepted a request! -_-
Thanks
btw, he has logged in since! I saw his post, and comment on a friends photo

[Tiffany]

Maybe he doesn't remember you or he cares about the number of people he follows. Or he might just be one of those people who don't follow back but its nothing personal on his part.

[Lujalixu]

Cyber stalk and cyber bug him till you get that motherfuckers attention.

Nuff Said!