The cause of an annuity's limited liquidity is primarily:
4. Surrender charges and potential tax penalties
Annuities often have surrender charges that apply if you withdraw funds before a specified period, which can limit your ability to access your money easily. Additionally, if you withdraw funds from an annuity before age 59½, you may also incur tax penalties, further reducing liquidity.
The other options (mortality costs, front-end loaded character, and poor investment results) may affect the overall performance and cost of the annuity, but they do not directly relate to liquidity in the same way that surrender charges and tax penalties do.