Why are most parents especially mothers struggling about their kids growing up?

My cousin is in high school and his mother is still struggling to get used to the fact that her son is in high school. In one of her post she said, "I can't believe my my oldest is a sophomore I college and I'm just getting used to my son being I high school so DONT JUDGE ME!!! 🤣😂"
I don't understand why mothers and father's have a hard time accepting that their kids are no longer little. My dad still tries to protect me and I'm 25. Yes I'm still his little girl. My dad one day was like, "Why can't you be that small again?!" Then I said, "Daddy why can't you accept and love me for who I am now? As a grown up." Then he said, "I don't need you to remind me that you're a grown woman. Shut up."
Most parents are so fiesty and blunt as hell.