Step-by-step explanation:
I believe it's mainly due to the muscle, the blood from the right ventricle is only pumped to the lungs whereas the blood in the left ventricle is pumped around the body. More force is needed for the blood to be pumped around the body hence why the muscles at the left ventricle are larger.
It's like basically exercising, the left ventricle works out more and it's about 3x as thick as all the other walls in the heart