Why can't I delete Facebook data?

Recently i found out the app was taking 2gb of storage in data alone, many here have asked for that, but haven't seen anyone mentioning my same problem of being unable to delete the data.

I wanted to delete it to make sure I would free up storage, but that didn't work, it would go from 2.41gb to 1.68gb, and only Facebook was being like that afaik, then I uninstalled it and thankfully the data was deleted, but not being able to delete it despite having the "option" was so odd.