Most apps seperate config and user data. I'd guess the reason for this would be, people primarily care about the user data (Photos). So the config data like user profiles/Album organisation are less important. The idea being, maybe immich turns into a dumpster fire and you want to use something else, at which point you only care about the photos.
So that app data, or config data as I called it are historically different, so additional work may be necessary.