Not everyone has an obituary, especially if they passed away many years ago or lived in a rural area. Obituaries are typically published in local newspapers or online, so if the person had no surviving family or friends, there may not have been anyone to write or publish the obituary.
Furthermore, in some cases, the deceased's family may have chosen not to publish an obituary for personal or financial reasons. So if you're really having trouble finding an obituary for a specific person, it's possible that one was never published.