i was watching a girl's live reaction to the same question:

https://www.youtube.com/watch?v=leyo5PWAyXI

It was eye opening to see how a girls responds rather than how a men could rationalize this behavior, like how the usual suspects are attention and as well as being suspicious character. It gets even worse as you go along the video and its logic, you see that most girls have a second social media account in where they hide very personal things in their life.

Like if your SO hides his social media accounts from you, doesn't that seems suspicious? Like he/she is hiding more personal relationships other than his/her family? But when most woman do it, its okay and somewhat rational hide it from your SO.

In certain situation, like endangering your SO, it seems legitimate but it falls flat when there are some men that want to show off their SO, not as eye candy but as a form of appreciation to one another and they have the thick skin for any drama that comes their way. In some answers you get a response in where most girls want to hide an abusive SO and don't want the drama/attention that comes with it: https://www.quora.com/Why-does-a-girl-hide-the-existence-of-her-boyfriend-from-other-friends-especially-male-friends. In where i don't understand that logic, like your relationships are your problems to solve, if you have an abusive relationship, cut them off or try to confront it. Why would that entail drama/attention? That only happens in the lowest of celebrity/e-celeb relationships where you get high-school-esque, he-said-she-said gossip and i think we can all agree that's not adult behavior.

In some subreddits, you get even dumb answers like r/AskReddit in where you get an answer where they don't want to hurt and ex's feelings like in: https://www.reddit.com/r/AskReddit/comments/129kty/taken_girls_of_reddit_why_do_you_hide_your/c6t9vif?utm_source=share&utm_medium=web2x

Its even worse in that if you go to female dominated subreddits like r/AskWomen, you aren't given a straight answer or they project a form of insecurity. Do you mind giving an answer why do most women do this? is it for attention? Is it to maintain a positive image, like chastity, party-girl image, or liveliness? I also appreciate if there is a certain level of seriousness in a relationship that goes with it, like are you more willing to hide you SO in social media when its somewhat causal like a boyfriend, but not when he is your husband. Does this happen to most girls when they are young but not as they get old?