Back in the day, every major female pop star had one: a male pop star (or two, or three or more) who loved her”at least on the record and on the charts. Over the years, Barbra Streisand had Neil Diamond, Barry Gibb and Bryan Adams. Diana Ross had Marvin Gaye, Lionel Richie and Julio Iglesias. Olivia Newton-John, Linda Ronstadt and Stevie Nicks had their pick of men (Andy Gibb, Don Henley, Aaron Neville, Tom Petty and John Travolta, among them.) Whitney Houston had Teddy Pendergrass, Bobby Brown, Enrique Iglesias and George Michael. Madonna had Prince. Celine Dion had Peabo Bryson and R. Kelly. Mariah Carey had Luther Vandross, and so did Janet Jackson.

But where did the love go? Though there have been scattered duet hits in recent years (Jordin Sparks and Chris Brown‘s “No Air,” Ciara and Justin Timberlake‘s “Love Sex Magic”), they are fewer and much farther between. On the Billboard Hot 100 dated March 19, 2011, “Don’t You Wanna Stay,” Jason Aldean and Kelly Clarkson‘s country chart topper, was the only traditional male-female duet, way down at No. 34.

I’d say that part of the blame lies with the faltering power ballad, which isn’t the chart force that it was in the days when Celine Dion ruled the airwaves. Consider pop’s leading single males: Both of Usher‘s and Enrique Iglesias’s two recent Top 10 Hot 100 singles have been not ballads but dance-oriented collaborations with rappers and, in the case of Usher’s “OMG,” Will.i.am. Chris Brown’s comeback-in-progress also has been harder-edged and boosted by male guest stars like Lil Wayne and Busta Rhymes, and of Justin Bieber‘s two Top 10s to date, neither has been a ballad, both were with rappers.

But it’s not just about what the public seems to want” it seems to be what the artists want, too. Why play the conventional good girl, duetting with Usher or Iglesias, when it’s so much more fun being bad? In the past year or so, both Rihanna and Katy Perry have gone Top 10 with rappers (Eminem and Drake, and Snoop Dogg and Kanye West, respectively). Meanwhile, Ke$ha went there with electronica hipsters 3OH!3 (after scoring her first hit riding shotgun with Flo Rida), and Beyoncé and Lady Gaga got there together.

As for the guys, boy-on-boy (or boys) rule: Bruno Mars with B.o.B and Travie McCoy, Jeremih with 50 Cent, Usher and Iglesias with Pitbull, Iglesias and Bieber with Ludacris. If it were 2001, Iglesias, or Ricky Martin, probably already would have zipped up the charts with Katy Perry and/or Rihanna on his arm. But it’s 2011, and just as every good girl wants a bad-boy rapper by her side, it seems the hit-making males would rather roll with the rough boys than mush it up with the ladies.

Will the power ballad survive the current disinterest in them? Can singing couples make a comeback? I’d be surprised if they didn’t. Pop music is cyclical, and if Jennifer Lopez can rise again, so can love (which, incidentally happens to be the title of J. Lo’s upcoming album, minus a question mark). All it needs is the right tag team to deliver it back into the public’s good graces and up the charts. I’d pay money to hear Pink and Adam Lambert together, but would the masses buy it? I’m not so sure, but wouldn’t it be just like them both to try and find out?