Their rates can also be fixed for a limited period, and then drop say, after the first year. If you don't like the new rates and want to withdraw your money early, heavy surrender charges could kick in and cut into your returns.
Plus, if you decide to opt for fixed lifetime payments, those payments will not rise to keep pace with inflation. As a result, the value of the money you receive will decline over time as inflation erodes the purchasing power of each dollar. So for example, if you retire young and plan to keep collecting annuity payments for a longer period of time, the purchasing power of your money could be a big concern.