One reason annuities are included as a possible financial option is to provide tax advantages.
The money you contribute to the annuity grows tax-deferred.
Annuities have compound growth, meaning all funds in the account continue to earn interest — even interest on interest already paid. That sum of money grows faster when it's tax-deferred because there's more money to grow. The taxes are then paid on earnings (not the principal) during the payout period.
There are other tax advantages to non-qualified annuities. There's no mandate for you to withdraw money from your annuity at a certain age — so the funds can continue to grow tax-deferred.
You can also decide the amount and timing of the payments you take for tax purposes.