I really don't know what to tell you but my S8+, my co-worker's S8 and my friend S8 all of them from T-mobile have the option and on the Quick Toggles by default.
So, seeing that the only thing different in yours based on the screenshots you posted and your comment that you are sure that you have seen it before on the phone, my only guess is that somehow that app you have on the Quick Settings, Talon Pull, is directly involved in the disappearance of the Rotation toggle. I mean, you know how this third party apps can work sometimes, to be able to show a quick toggle for an app, the code must edit somehow the system file that works with that, so like I said above my only guess is that by installing that app it may have caused a corruption or simply in order to show a new one, a default one must be replaced.