In "Hard Times," what is the cause of Louisa's combined state of apathetic depression?
I think that there can be many reasons to attribute to Louisa's condition at the end of Dickens' work. I am inclined to place much of the blame for her condition at her father's feet. Gradgrind's teaching and rearing of Louisa was full of calculation and "fact, not fancy" that there was nothing significant in terms of emotional or sentimental education left over. The bizarre utilitarian philosophy of Gradgrind compelled him to educate Louisa in such a way whereby there was nothing in terms of emotions fostered or affect nurtured. In this, her arranged marriage was done in terms of facilitating not a marriage between two people, but a business alliance. Her devotion to her brother, the other victim of Gradgrind, compels her to undertake a disaster such as marrying a man so much her senior without any semblance of love or emotion present, a move that helps to cause her to lose any passion for living or love of life:
...her [Louisa] rearing has left her so lacking in any genuine feeling (apart, that is, from her passionate devotion to her brother), that she doesn’t care what becomes of her.
In the end, her father has to be the cause of such a condition because of his failure to teach her the role that emotions play as one progresses through life and consciousness in the world. It is because of this that the ending of the novel finds her engaging in philanthropic endeavors, hoping to bring some light and joy to those who endure suffering and pain, not so different than what she went through as a child.