On facebook it’s uncommon to use a facename. Not only that, it’s a TOS violation. A few years ago they started challenging people that started using even fake middle name (Steve SteelersGonnaWin Smith) by asking for a picture of their ID to prove it. I don’t think anything ever became of it, but yes, most everyone uses their real name on FB.
Your real name, bajillions of tagged pictures, facial recognition, brands/music/TV shows/movies/artists that you’ve ‘liked’ so they can target you with ads along with everything else. Google must be making them an offer (at least unofficially) on a somewhat regular basis.