Why can't I live without my smartphone?

Because you have relied upon it for so long that you don't want to think of having to remember all that stuff without it. Smartphones are good at training us not to think any more :)

Because it has grown attached to your hand.

Cuz you don't wanna

You and the majority of the world lol. There was a time they didnt exist , that time of life was happy

It's called addiction.