Why dont earthquakes occur in the aesthenosphere

Well Asthenosphere is not a solid layer like lithosphere. It is flexible therefore there can not be any force accumulated to generate earthquakes.

an earthquake occurs when one of the earth's plates suddenly slips past another. This does not happen in the asthenosphere because it is molten and there are no solids to create friction, get stuck and slip suddenly. however, some of the waves from an earthquake will pass through the asthenosphere.