Why Dont Earthquakes Happen Everywhere At Once?

This because in most places that arent near plate bounderies you can't have earthquakes so that is out of the question though other countries might not because its something usually caused by a disruption to nature that makes the earthquakes which is why you  don't get them all over the place at the same time  not at the same time everywhere something disrupts nature.

Earthquakes only happen along plate boundaries and fault lines.

They weren't created to go off at once .