I think it is particularly true when one starts to identify with the illness. You become th illness. You know what to expect from it. Health? What the blazes can one expect from that ? I really think thought that the reasons for defending it can vary greatly from person to person. It can be fear of success, entitlement, an odd sense of revenge, a sense of identity, a feeling that one draws creativity or strength from the illness, any number of things. People are different.