Why is guitar music so popular nowadays ?

Well ?

You'll have to be more specific.

Music with guitars in it is pretty broad. Even rap has guitar samples included. Any genres in particular?

I mean- indy,beat rock ,generic rock,soft metal etc.

Because cheesy pop music has run its course, and clean accessible indie-rock has replaced grunge/metal music as the most common form of guitar music, making it less of a niche category and more likely to break into the mainstream.

Nowadays?

Rock music has always been popular. It's timeless.

EDIT: Ok, since it's inception in the 50's at least.

Because it's cool.