Is there a reward for guardianship (qawamah)? If so, is it great? Is the absence of a reward for it considered an injustice to males? Does its association with financial support justify the preference, despite it being a heavy responsibility?

The Sharia has not wronged men or women, and Allah does not desire injustice for anyone in the worlds. Indeed, His Sharia is entirely mercy, wisdom, and benefit. One must submit to the command of the Sharia, and if the wisdom is not apparent, then be certain that it exists. Guardianship (qawamah) includes looking after the affairs of the woman, reforming her religious and worldly matters, enjoining good upon her, and forbidding evil from her; this carries a great reward. A Muslim is rewarded for his spending on his family, for his efforts in earning for them, and for treating his wife with kindness and excellence. Allah does not let the reward of those who do good go to waste.