Why are earthquake considered spot things?
Faults and discontinuities within the Earth's crust are rarely smooth and any smooth parts are short in length.

The degree of roughness along a fault or any discontinuity varies in strength and magnitude. This causes stresses to build up unevenly along faults and discontinuities. When the stresses are too large for one rough patch to withstand there's a break and stress is released causing an earthquake. This is why earthquakes occur at a particular location.