This is because in permanent life insurance some of the money is put into a savings program.
Therefore the longer the life insurance policy remains in force, the higher the cash value, because more money has been paid in and the cash value has earned interest, dividends or both.
The debate is all about that cash value. If you buy a life insurance policy today, your first annual premium is likely to be much higher for a permanent life policy than for term.
However, the premiums for permanent life insurance stay the same over the years, while the premiums for term life increase. That extra premium paid in the early years of the permanent policy gets invested and grows, minus the amount your agent takes as a sales commission. The gain is tax-deferred if the policy is cashed in during your life.
The saying you always hear is, "Buy term and invest the difference." The fact is, it depends on how long you keep your policy. If you keep the permanent life policy long enough, that's the best deal. But "long enough" varies, depending on your age, health, insurance company, the types of policies chosen, interest and dividend rates, and more. The reality is that there is not a simple answer, because life insurance is not a simple product.