Ask the many Mormon male youths forced out of Fundamentalist Mormon societies where polygamy still is practiced (e.g., Colorado City, AZ); the older male hegemony wants a monopoly on the "upcoming crop" of coming-of-age young women. (My statement reflects that hegemony's commodification of women, not my own.)

You might object that marriage in itself is an outdated/outmoded, and we should all live polyamorous lives. Marriage has been a relatively stable social/legal contract for millenia, and I think attempts to make it irrelevant or obsolete will always fail.