Accidental Death and Dismemberment insurance (AD&D insurance) pays for death due to accident, such as falling down stairs or being in a car wreck. Life insurance pays for death due to accident AND natural causes, such as cancer or old age.
The reason Accidental Death insurance usually costs less than Life insurance is because the number of people who die from accidents is a fraction of the number of people who pass from natural causes.
With the exception the insured dying at the hands of the beneficiary, the insured committing suicide in the first two years of a policy, and any contractual war clause exemptions; life insurance pays the death claim whether by accident, disease or natural causes like old age. Accidental death or AD&D (accidental death and dismemberment) pays only accidents not disease. AD&D is less expensive because the actuarial accidental death statistics are so much lower than death caused by disease.
The reason Accidental Death insurance usually costs less than Life insurance is because the number of people who die from accidents is a fraction of the number of people who pass from natural causes.