Shell integration is registered in more than one way, and an uninstaller generally removes only the specific registrations its build knew about. Several common situations produce leftovers.
The first is surface drift across versions. An application that originally shipped a classic shell verb and later moved to a COM handler, or added a packaged modern-menu command, ends up with registrations from more than one era. The current uninstaller cleans up the current mechanism. The older registration is not in its list, so it stays.
The second is hive mismatch. A registration written machine-wide requires elevation to remove. If the uninstaller runs without it, or the user declines the prompt, the removal quietly fails while the uninstall itself reports success. The same happens in reverse: an app installed per-machine but run per-user can leave a per-user registration the machine-wide uninstaller never looks at.
The third is registration under file-type associations rather than under the application's own class. Archivers and media tools frequently register against many individual extensions. Removing the app's primary class registration leaves the per-extension ones intact.
The fourth is simply incomplete uninstall logic, which is common in small utilities and portable applications that were never really designed to be removed cleanly.
The consequence for you is that "reinstall and uninstall again" usually does not work, because the second attempt has the same gaps as the first. What does work is identifying the surviving registration directly and disabling it. ContextCleaner treats these entries like any other: it shows where the registration lives and what it points at, and it removes it non-destructively so the action is reversible. That last part matters more than it might seem, because an apparently missing target file is not always proof of an orphan — a path on a disconnected drive or network share looks identical to a deleted one. Making the removal reversible means a wrong guess costs one undo rather than a reinstall.