Sometimes we just have to guess why an area has earthquakes, but general either an active fault, an active volcano, or an active geothermal area will have some quakes.

As for why a particular volcano has quakes, we generally associate quakes with ground deformation, so magma might be flowing, magma chambers might be filling, faults might be shifting as the pressure rises or falls.

Vague enough to stay out off the hot plate on this issue?