Another issue is, as women, we kiss you and we fall in love a little; we sleep with you and we fall in love a lot.
Modern society is virtually built on sex, and it's such a mine-field. Not having sex before marriage can prevent heartbreak in a way being in a sexual relationship can't. Being heartbroken is the fastest way to take your eyes off God; nothing hurts as bad, does it? Nothing on earth can make someone crumble like being heart broken, and during those times, it's very very easy to take your eyes away from God and turn them inwards. I think God is preventing that by mandating we don't sleep with someone until we're married.
Society has indoctrinated us all into believing if we're not having swingin-from-the-chandeliers-sex every day with multiple partners we're a loser, but that's simply not the case. Sex is something beautiful; sharing your life with someone who fits you perfectly is something beautiful; what's the harm in preserving yourself for your Person? To a Christian, yes, it's another way of glorifying God, but even to secular people, what's the harm in waiting?