Mariah Carey, who made her debut alongside Nicki Minaj and Keith Urban in the now-storied role of celebrity judge on “American Idol” on Wednesday night, was paid as many millions as she has lifetime No. 1 hits  (18) to appear on this, the twelfth season of the long-running show. Eighteen million also happens to be the approximate number of viewers who tuned into the season premiere of the Fox show, down from 30 million just three years ago. That paycheck and even the lackluster ratings still put her ahead of Britney Spears, who received a reported $16 million for her one season of judging on rival “The X Factor” this fall (a brief experiment that will not be repeated). Her debut episode drew even less interest than Carey’s, resulting in what was then the lowest ratings ever for the show. The Spears hire was, more or less, a direct reaction to the attention-grab of her longtime rival Christina Aguilera, on yet another singing-competition show, “The Voice.” Both Aguilera and her former co-judge CeeLo Green (of Gnarls Barkley and “Fuck You” fame) decided not to return to the show this season, instead opting to focus on their own recording careers for a while. Their slots have been filled by Shakira and Usher. Elsewhere, channel-surfing after 8 pm in the past few years, you might have encountered Steven Tyler, Adam Levine, Jennifer Lopez, Blake Shelton, and Demi Lovato on a judges’ panel.

The Celebrity Judge, in other words, has become a staple, and, in recent years, the celebrity half of the job description has become far more important than the judge part. (Since Aguilera’s initially surprising participation – regarded when she signed on as a new low, but which turned out to be quite the opposite—it has been a gig increasingly filled by A-listers.) He or she is trotted out before the cameras like an animated trophy, mostly to remind the viewing audience and the hopeful contestants that the brass ring exists. After all, both Spears and Aguilera appeared on “Star Search,” a previous generation’s version of the high-stakes talent show. Someday, with a lot of luck and talent and hard work, those contestants can end up on exactly the same prime-time cattle call—only next time, it’ll be for pay. This might seem to be the natural order of things, but in fact, the degree to which the trend has overtaken the shows represents the closest thing the celebrity-industrial complex has seen yet to an existential threat. (Breathe. It’s unkillable, even at its own hands.)

The celebrity-judge gravy train began with Paula Abdul, back when it was more of a D-list kind of occupation. She, with her career long stalled, needed “American Idol” more than it needed her. And it worked. Soon, every American with a television set knew in 2002 that she was the sweet, and possibly addled, foil to Simon Cowell’s mean-guy truthteller. Cowell, by the way, belongs to a rarer genus than the Celebrity Judge: a judge turned celebrity. (In case anyone ever asks you what Tim Gunn and Richard Posner have in common, you’ll want to remember this category.) Cowell became famous the honest way: he was not only distinctive, but the very best at what he did. He cared about the performances, offered incisive critiques, and often bet on less marketable singers whom he thought were more talented than their rivals. Simon and Paula may have argued (and flirted) with one another, but mostly Paula was there to break up the tension, which was always, really, between him and the contestants on stage: What would he say to them? How cutting would he be? (Randy Jackson, then as now, was … there.)

Still, Abdul’s success, which she managed to bite off without any evidence whatsoever of fangs, established that any celebrity who agreed to such a gig needn’t worry about lowering her Q score by doling out harsh criticism to the average Americans with above-average pipes who appeared before her. Reality show contestants might not be there to make friends, but celebrity judges—even, now, Cowell—are.

Consider Carey’s guest-judging appearance on a previous season of “Idol,” which presumably functioned as her audition for the large contract she signed for this one. “I feel weird about the whole, like, ‘judging’ people in general,” she said, with air-quote gestures abounding. “Just look at me like, whatever, that’s my friend I met last week who sings for a living and writes songs occasionally,” rolling her eyes both casually and shrugging for extra effect. “I’m glad I got to see these guys now because who knows what’s going to happen," she continues, with unconvincing generosity of spirit. “We’ll see them, ah, see them hopefully at the top of the charts, every one of them,” now with a shimmying little movement of her head, and a wide diva grin that assures the viewer she isn’t currently threatened by any of these upstarts, but if they get any closer to success, shivs might be out.

Because that’s become part of the script: celebrity judges can’t be mean to the actual contestants, but they can be mean to each other. Or flirt wildly with one another. (Just about everyone took a crack at country heartthrob Blake Shelton, though perhaps they might do well to look up one or two of his wife’s hits.) Beefs, like the one that the Fox PR department seemed determined to gin up between Minaj and Carey, and one which the ladies are only too happy to enact on camera, appear to be the next front in an increasingly desperate attempt to re-up interest in the show. Or, more to the point, to re-up interest in the careers of the judges themselves.  Judges log a whole lot more time on stage performing than they used to, and other established stars, like Taylor Swift, make frequent guest appearances. 

Meanwhile, new roles have been created to give the maximum number of celebrities an opportunity to align themselves with the brand. On “The X-Factor,” Cowell’s current vehicle and the most fame-obsessed of the trio, there are now celebrity “mentors” (Justin Bieber, Marc Anthony) in addition to judges—which requires less time commitment but still brings a certain amount of “prestige,” something loosely akin to being of counsel at a law firm—as well masters of ceremony who appear to have been picked out by a network executive throwing darts at an Us Weekly. (Not the bullseye, but guess we’ll settle for the tall Kardashian!) Much of the press around the show has shifted away from the contestants, who used to become true bold-faced names by the end of the season, and towards to the judges: how they interact with each other, who is going to sign up, and for how much. Publicists have gotten good at floating rumors about some of the world’s most bombastic personalities. Kanye West, Charlie Sheen, and Diddy’s names were all bandied about this summer, more unlikely for the chaos they would have created than for the salaries they would have commanded: none would have been docile enough to say the boring or scripted things expected of them.

What made “American Idol” feel so new a decade ago, despite the timeworn premise of a talent search, was that it promised to reveal how your celebrity sausage got made. Everyone’s gorged themselves on the end product, but how’d it end up on your plate? Who was making those calls, and what did those appraisals really sound like? Having talent and judging talent are not the same thing, which was the dynamic upon which the whole enterprise rested. With a few exceptions (Christina Aguilera is a range snob, for instance), the pop stars on the panels these days often don’t seem to be much more musically discriminating than the audience at home.  

Yes, the three shows’ tanking ratings are at least in part a result of having diluted the market among themselves, but whoever is making the casting decisions upstairs at the network—the decidedly noncelebrity judges picking the onscreen talent for a very specific kind of role—has made the crucial mistake of forgetting that anyone who has tuned into the show has done so, on at least some level, because the existing universe of pop stars isn’t quite enough for him. Nicki Minaj might be doing her best Nicki Minaj, and Adam Levine might be doing his best Adam Levine, and Steven Tyler might be doing his best Steven Tyler, as they were all hired to do, but the viewer already knows well what that looks like. He’s sick of the old meat gumming up the grinder. He wants something fresh.

No one tell Mariah that, though. At least not in range.