I'm not sure if you can disable comments on Facebook or Twitter, you can set as "private" your account but then on facebook you have to accept one by one the people who want to be your "friend" and something similar happens on Twitter, too much trouble and not even fans could see her pictures, Ig allows just to block the comment section but you can still see or like her posts
besides, Ig had a lot of haters and people commenting rude things on her pictures unlike FB or TW (there are some trolls as well but is less common)