Doctors set up group surgeries to have loads and loads of people on file, registered with them. They have no wish to see these people, from one year to the next, as that would mean working!! They group practice pools the names registered and operates as a partnership. They employ out of hours and week end agencies and the fees involved are tax deductible against their income.
Their income is derived from the set amount of money per head registered and so it is not in their financial interests to report them dead, even if they know that for a fact. Of course, if they have never seen their patient, they merely assume that he/she needs no help. They never check if they are living at the file address or if they are alive.
If a patient moves from one surgery to another there is a credit and debit situation. But most people move home and only worry about doctors when they need something and so their registration remains at their first surgery.