So then, the Mahr is Islam’s version of the Dowry.
Only one step removed from the outright “selling” of your daughter to the highest bidder, similar to selling livestock or slaves.
In strict Islamic societies, women have little economic value, other than as wives. Hence the practice of child marriage: the younger the girl gets married, the sooner the parents can stop feeding her and let the husband support her.
This also explains the practice of honor killing. A non-virgin becomes economically valueless, so might as well kill her.