What commercial auto Insurance Cover should I buy? Why is a comprehensive policy more expensive than liability only?

In India, third-party liability insurance is a mandatory buy for all vehicles plying on the roads in India. The liability-only policy covers losses and damages to people and property caused by the insured to others. A comprehensive policy covers both ‘third-party liability’ and damage to the insured’s own vehicle. A comprehensive policy is broader and therefore more expensive than a liability-only policy.