Insurance companies mainly rely on three price differences to make money. The so-called "three differences" include: fee difference, dead difference and spread. "Three differences" refers to the difference between the actual cost, actual (insured) mortality and actual investment income and the expected cost, mortality and investment income when an insurance company designs a policy, which is simply the difference between "budget" and "actual".
Further reading: How to buy insurance, which is good, and teach you how to avoid these "pits" of insurance.