Usbek is lord and master of his many wives. He lives in a traditional society in which men are in complete control, and women are expected to be silent, demure, and to do what their menfolk tell them to do. Women are also expected to be chaste and sexually continent. The prevailing double standard holds that, though it's perfectly fine for men to have multiple partners, women must remain faithful at all costs. Not to do so is considered deeply shameful and dishonorable in this male-dominated society.
Usbek's concern for his wives' chastity can be seen in the letters he writes to the Chief Eunuch in charge of the harem. As castrated men eunuchs were thought ideal to be placed in charge of a separate part of the palace reserved for women. In his letters to the Chief Eunuch, Usbek constantly urges him to keep his wives firmly under control and do whatever it takes to protect their purity. Usbek doesn't like the idea of his wives being given too much freedom, and although he allows the Chief Eunuch to take them into the country, he tells him that the women must always be reminded of how powerless they are. This is somewhat ironic as the Chief Eunuch is a slave with even less power than the women he's supposed to be controlling.
Usbek may have abandoned his wives, but he's still determined to exert control over their lives from a distance. He must maintain the dignity of his reputation, and that means making sure that his wives always act according to his wishes. This isn't a relationship of equals by any stretch of the imagination, and it's interesting that the wives attempt to change its dynamics by fairly drastic means, staging a rebellion against Usbek's stifling rules and restrictions, which are pretty extreme even by Persian standards.