Don't get it. Why not get a real computer?
When you're waiting at a train stop, it's easy to pull out your phone and browse. Not so your laptop. Similarly, when you're waiting for your order to arrive at a restaurant, you pull your phone... Quickly, it becomes a reflex to just pull out your phone when there's nothing going on, or when you want to change your mind... then it ends up being when you're in bed about to sleep but want to look something that crossed your mind...
I'm stating the obvious, but your question is kind of weird. It's kind of asking "Don't get it. Why not smoke weed" on an article about alcoholism.
This is me, unfortunately. I need to get rid of this urge, but it's s damn hard. I'm glad I banned phones from the bedroom, I really seem to be able to fall asleep much better, most times. But in all the other scenarios, that's me, pulling out my phone to have something to do. I can't even remember what I used to do while waiting for stuff. Then again, I've had smart phones for the past 13 years, so that's pretty much all of my grown up life.
None of this is impossible to get around though, I could get a small camera and there are alternatives to Google Auth.
Also, the law wasn’t enforced that well. There are still some PC bangs which don’t kick out teenagers late at night, and those fun-hungry high schoolers will always find a loophole for these kinds of stuff. (For example, the law is impossible to enforce in software, because even with online multiplayer games you can easily make a overseas account through a VPN.)