Why are usurious interests given to the poor, and are they fundamentally their right?

Usurious gains are forbidden to the usurer and must be returned to their owner, based on the Almighty’s saying: "But if you do not, then take notice of war from Allah and His Messenger. But if you repent, you may have your principal sums. Do not wrong, and you will not be wronged." If it is not possible to return them to their owners, they should be spent on general Muslim welfare, such as orphanages and hospitals, or given to the poor and needy.