what does the 3rd amendment have to do with anything if we're just agreeing it's bad for private companies to do it? Like, the 3rd amendment specifically exists

what does the 3rd amendment have to do with anything if we're just agreeing it's bad for private companies to do it? Like, the 3rd amendment specifically exists to specify it's _also_ "bad" (and illegal) for the government to do something you wouldn't let anyone else do.