Explain why tectonic activitys happen along the plate boundaries rather than in the middle of a plate

Tectonic Plates and Plate Boundaries

You can actually see New Zealand’s plate

The Earth’s outer shell, the lithosphere, consisting of the crust and uppermost mantle, is divided into a patchwork of large tectonic plates that move slowly relatively to each other. There are 7-8 major plates and many minor plates. Varying between 0 to 100mm per year, the movement of a plate is driven by convection in the underlying hot and viscous mantle.