Medical histories are useful when thinking about diagnosis and management. The problem is that they're rarely accessible in a concise or summarized format. Medical systems produce huge amounts of paperwork, even a simple day trip to an A+E department will produce about 30 sheets of paper, and there's no automated way to extract the pertinent information from that. Its much easier to just ask the patient about important things in their medical history, and if any of the previous diagnoses are particularly significant you can delve into the previous records.