Because it's inaccurate. After a while it's going to gain or loose a couple of seconds. I have a couple of G Shock, some with solar rechargeable and atomic rad

Because it's inaccurate. After a while it's going to gain or loose a couple of seconds. I have a couple of G Shock, some with solar rechargeable and atomic radio sync. Even when in countries with no atomic radio signal I can sync my laptop using ntp and use a Java program + headset / speaker to mimic atomic radio signal to sync my clock automatically.