Question

how do ventricles have thicker walls than auricles

Answer 1

Atria (singular Atrium) (and auricle is actually a part of the atrium), have to just push the blood from within them into the adjacent ventricle.

While the ventricles have to pump the blood far away, upto the distant toes and fingers (left ventricle) and corners of your lungs (right ventricle)

The left ventricle is about thrice as thick as the right ventricle, again the reason for this difference is because the right ventricle has to pump blood to the nearby lung only, while the left ventricle has to push it out to all other organs, far and near to it.

In patients whose heart (left ventricle) is unable to pump blood to the extremities efficiently ( a.k.a. Left Heart failure ), the thickness of the left ventricle further increases ( called left ventricular hypertrophy ).

All these changes is thickness is seen only in the middle layer of their heart wall ( myocardium ), while the other two, outer epicardium and inner endocardium are of same thickness in all places ( yeah yeah they are just a few cell thick )

Answer 2

ventricles have to pump the blood into various organ so they have thick walls than atrium