Someone who worked in tabloid celebrity news many moons ago (pre-internet, or at least pre such things being dominated by the internet), explained to me how things worked. It wasn't that they always "got it right," but the better publications did have some boundaries and rough codes of conduct. First, the public/private figure distinction is important. Not so important for tabloids that mostly traffic in celebrity gossip, but even with them there are non-public figures who can get caught up in celebrity stories as parties to whatever the story is. That's a consideration. And, second, the dirty little non-so-secret is some celebs use the tabloids as PR outlets, and some don't. So there's a bit of live by the tabloid, die by the tabloid. If you publicize the details of your public life as a way to promote yourself (or your publicist does), then the details of your public life are much more fair game generally.
Not saying all of this is perfect, but there's a certain logic to it.
