Hermione may feel a deep sense of empathy for Severus. After learning about his difficult past, she wants to give him a family and a sense of belonging. She might think that having a baby would be a way to heal his emotional wounds and also create a new family unit that is based on love, understanding, and mutual respect. This would also be a way for her to show the wizarding world that people can change and be loved despite their past mistakes.
Hermione might see Severus as a very intelligent and powerful wizard. She could be attracted to his knowledge of the Dark Arts and Potions, and think that their child would inherit great magical abilities. Also, Hermione might believe that she could redeem Severus through their relationship and having a child together would be a symbol of that new start.
For Hermione, it could be about breaking boundaries. She has always been a rebel in her own way, challenging the norms of the wizarding world. Loving Severus and wanting his baby could be her way of showing that love can transcend age, past enmities, and house differences. She might see in Severus a kindred spirit in terms of their love for magic and their complex natures.