The issue is this: They are public figures. Same thing with actors and singers. Unfortunately it comes with the territory. There are plenty of actors and producers/directors whose acting/directing/producing skills get REALLY criticized. Ever read the webpage, "Rotten Tomatoes?" They destroy actors and producers. They saw pretty mean stuff about movies they dislike. Do you ever hear producers calling people on Rotten Tomatoes, "haters." Nope. Ever hear Tom Hanks call a movie critic a "hater" when they tear up a movie of his? Nope.
To a great extent, this is exclusively a bodybuilding thing. Biggest cry babies out there.
Yes, they are public figures, but nobody forces them to use social media all the time. Once they start doing this, most of them get infected by that 'hater-bug'.
Take a look at Dennis Wolf. He does some vids for MD and that's about it, simply because he isn't so attention obsessed as Phil. He's one of the most likable guys for being a humble, approachable and easy going guy.