Someone please explain this to me

Okay so i'm not trying to bash anyone because I respect a mothers choices 
But heres the deal , my friend had her baby yesterday , and on instagram she posts pics but of her babys body not of her face and of the back of her body+head but again not of her face 
and someone asked her why doesnt she show her babys face and she said " because I dont want people on here seeing her to see her face " 
But on some other app she does post the babys face. 
So im wondering why not on instagram? Her page isnt public and if you dont want people that are following you to see your babys face then why cant you just unfollow and block them ? Also you can choose who's request to accept or deny. 
Its not my business but I dont really understand that. And like I said I don't blame anyone I know a lot of moms who say they don't want their childs face on social media . Me well I'm no one to say anything because I have not posted anything on my instagram about my pregnancy and i'm due next month I just posted one ultrasound but since I have a bunch of followers that I dont know nobody commented on it but when I have my daughter I will be posting pics of her , Just because I don't post pics right now doesnt mean im embarassed by it. 
So can someone please explain , Whats your reason to do it or to not ?