I honestly am so confused. 🤔

I'm not saying any of this In shame but in Curiosity. Why do some mothers that have problems with their baby's father do not allow the dad to see the baby in any way. My brother has a daughter and his baby mother and him weren't ready for a child at all and she uses the child against him a lot, I know also she won't let my bio mother see any picture or let her know anything about the baby as well as my brother. My mother provides diapers for her and wipes. I'm not shaming her just simply saying the truth and I'm honestly confused why some women do this. I know In some circumstances it's to be safe if the father is abusive and what not but my brother and mother weren't and aren't. I know it's her child and understand that. I also know for sure she will as soon as my brother and her

Get back together have no problems with him or my mother, my brother knows honestly they won't work out. I just want to know other reasoning for someone who actually does understand why to help me out