Compared to that, these women get a good deal, at least they get paid, and probably can break the "contract" if the so called "man" beats them.
Of course I don't imagine being party to such an arrangement does much for the woman's possibility of a more permanent type arrangement. Maybe as wife #4 or something.
The ease of divorce in Islam is actually the corrupt and corrupting thing here. A mutaa is at least honest to the woman: she knows it's not going to last.
It is a Shi'ite institution, and, despite the lunatics currently running Iran, Shia has usually been the more civil and civilized branch of the false creed. Doubtless some imam or mullah way back when noted that women were getting screwed in the metaphorical sense (the literal sense being obvious) by men who married them with the intent of divorcing them after a short time, and decided to make the whole thing more honest.