The cache plugin type prevents any store plugin from being uninstalled, even though only 3 of them are required (file, session, static). This has some negative consequences for server administrators, not least that third party store plugins that are no longer used (or possibly even supported) can't be removed.

It would be much better if only the required default stores couldn't be uninstalled.

It seems particularly strange that this is prevented given that Moodle continues to work as normal even if a plugin is uninstalled while in use (give or take a debug message or two)!