My great-grandfather was ill for the last several years of his life. Bedfast, his wife and children cared for him in their home for several years. His condition finally reached a point where the family could no longer care for him at home and he was sent to a state hospital several counties away where he died in 1934. His obituary indicated he died at home and his children in later years made similar statements. No one wanted to admit that they couldn't "take care of dad at home" at the end of his life.
Is there a similar reason why you can't find great-grandpa's death certificate?