Rejected funeral policy by the unlimited

My late Mother had a funeral policy with the unlimited since 2017, she passed away in July 2020 I tried to claim but east London office was always closed. I lodged my claim in august few weeks back I received a call telling me that claim have been rejected because she was diabetic and they don't cover pre existing condition. Why would my mother take a policy knowing that she is not covered. She was diagnosed with diabetic in 2016 but took the policy in 2017.