Why does someone with metastasized adeno non-small cell PD-L1 Carcinoma, that is approved for SSDI not get full Medicaid coverage or any Medical insurance coverage? When someone who gets SSI automatically does?

Blows my mind that someone with a condition that could end in death, yet worked up to the day they were diagnosed with this life ending condition does not get Medicaid or any insurance. With a diagnosis like this it should be automatic before people who get SSI. They have worked all their life and now need help and can't get it!!!! Something is very sadly wrong with this picture!!