A few years ago, A. O. Scott of The New York Times suggested that for explanation we need look no further than the names just mentioned and others like them: the downslope from Katharine Hepburn to Katherine Heigl is simply too steep, and “the few remaining stars who show the kind of audacity and charisma that great romantic comedy requires tend to be busy with other things.”

This is certainly true, but it in turn begs the question of why today’s genuine stars (with all due respect to Kate Hudson and Matthew McConaughey) no longer bother to find the time for romantic comedy. Will Smith, for instance, displayed tremendous chops in Hitch—but apart from that toe-dip, he’s stayed clear of the water. And this generation’s most obvious fit, George Clooney, has modeled his career on that of Cary Grant in almost every way save his profound reticence to explore the genre that made the latter an icon.

No, there’s more at work here than the vagaries of stars or studios. It’s not just them; it’s us.

Among the most fundamental obligations of romantic comedy is that there must be an obstacle to nuptial bliss for the budding couple to overcome. And, put simply, such obstacles are getting harder and harder to come by. They used to lie thick on the ground: parental disapproval, difference in social class, a promise made to another. But society has spent decades busily uprooting any impediment to the marriage of true minds. Love is increasingly presumed—perhaps in Hollywood most of all—to transcend class, profession, faith, age, race, gender, and (on occasion) marital status.

When Sydney Pollack, for example, made the disastrous decision to update the Billy Wilder classic Sabrina in 1995, one of the remake’s (many) flaws was its failure to modernize the obsolete dilemma of the rags-and-riches romance. As Samuel Taylor, who wrote the original Broadway play and collaborated on Wilder’s script, told The New Yorker at the time, “If they really wanted to make it interesting, they’d find a really good black actress to play [Sabrina].” Eighteen years later, of course, that wouldn’t be enough. She’d have to be a mummy.

Perhaps the most obvious social constraint that’s fallen by the wayside is also the most significant: the taboo against premarital sex. There was a time when carnal knowledge was the (implied) endpoint of the romantic comedy; today, it’s just as likely to be the opening premise. In 2005’s A Lot Like Love—a dull, joyless rip-off of When Harry Met Sally—Amanda Peet and Ashton Kutcher meet cute by having sex in an airplane lavatory before they’ve spoken a single word to each other. Where’s a film to go when the “happy ending” takes place at the beginning?

Serious obstacles to romantic fulfillment can still be found—illness, war, injury, imprisonment—but they have a tendency to be just that: serious. There aren’t likely to be many laughs, after all, in the story of a love that might be torn asunder by an IED. It is perhaps no coincidence that romantic melodramas (such as last year’s The Vow and the recent epidemic of Nicholas Sparks adaptations) are doing quite well at the multiplex even as their comic siblings falter.