Partner shaming????

I really don't understand why there is so much partner shaming and shit talking about the person who your supposed to love or at the very least care for??? It doesn't make since to me. I mean if your partner knew that you were bad mouthing them on social media wouldn't they be hurt and upset? Would they even want to be with you anymore if they found out you were airing your personal business and bad mouthing them??? I know I would be livid and hurt! It's not mature or appropriate in my eyes. I mean if you are adult enough to be in a relationship the why can't you talk to your SO instead of talking bad about them? I love my husband more than anything in this world and would never say a negative word about him to anyone BC I never want to hurt him and vise versa... Wouldn't it break your heart if the shoe was on the other foot? If someone you care about was talking bad about you and telling social media about your private issues?