Why isn’t Britney Spears’ latest album a hit?

When Britney Spears releases an album, it’s an event powered by dizzying promo plugs and more hype than even Gaga’s been able to muster.

All this usually means a debut at the top of the Billboard 200 and impressive sales stats to tack onto the already lengthy footnotes for one of pop’s biggest stars.

But Spears’ latest album, “Britney Jean,� may be the disappointing exception to her platinum-lined rulebook.

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A week after its release, the album isn’t sitting on top of the charts. Instead a box set from Garth Brooks snagged the pole position, and the pop singer landed at No. 4.

Opening within the top 10 is noteworthy in an age of fickle record buying, but Spears is expected to perform better than this.

“Britney Jean� is the only new release to land in the top 10 this week, yet it’s behind Brooks, One Direction’s latest and a recent Christmas album from Kelly Clarkson.

It’s the sort of debut that music pundits would declare a flop, especially considering how a slew of the post-Y2K pop divas Spears once laid the blueprint for -- Lady Gaga, Katy Perry, Miley Cyrus -- all fared much better with their albums this year.

Even more difficult to ignore: “Britney Jean� had the lowest-selling first week of any album in Spears’ career. Her last album, 2011’s “Femme Fatale,� opened at No. 1 after selling 276,000 copies, more than double the 107,000 copies that “Britney Jean� tallied.

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Granted, Team Spears is primarily focused on her upcoming Las Vegas residency, and understandably so. The ambitious gig – anchored at the Planet Hollywood Resort & Casino – will see the singer performing amid a flashy, high-concept spectacle (50 shows a year through 2015 are expected).

“Britney Jean� could get a boom when Spears opens in Vegas at the end of December -- but that’s incredibly unlikely.

So what happened?

The album’s lead single, the cheekily titled “Work Bitch,� has the DNA of a Spears hit. It is a throbbing jam tailor-made for weekend clubbing and voguing, with a punchy chorus and a sexy music video. It heated up the dance charts pretty nicely, peaking at No. 2, but it failed to crack the top 10 on the pop chart as audiences gravitated toward comeback singles from Gaga and Perry.

Its follow-up, the breakup slow-burner “Perfume,� fared even worse. The song is currently languishing at No. 79 on the Hot 100, and fans, dissatisfied with the single’s video, have launched a petition for the director’s version of the clip.

Also not helping matters was Spears largely being MIA. She’s done a slew of interviews filled with softball questions, but her bread and butter has been live spectacle, and she hasn’t done anything by way of live shows to keep that interest going.

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Imagine how much more fun the MTV Video Music Awards or the American Music Awards could have been with a splashy number from her? This too is likely another casualty of the pressures of prepping for an intense Vegas run.

Worse, however, was “Britney Jean’s� lack of Britney Jean.

In news materials announcing the album, and subsequent interviews from Spears, the album was touted as her most personal and revealing to date, after a highly publicized breakup with her fiancé.

It’s a routine promise from performers peddling a new record, but she kicked it up with a handwritten letter to her fans, and the album’s title is her nickname used by her family and friends (she’s already had a self-titled record).

Spears co-wrote most of the record -- the last time she was credited with co-writing the bulk of an album was her seminal 2003 effort “In the Zone� – and she called on electronic dance kings like Will.i.am, David Guetta, William Orbit and Diplo to build beats.

But not much was revealed on an album touted as a stripped-back look into the life of one of pop’s biggest names.

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Times pop music critic Randall Roberts wrote in his review “if this is Britney in revelation mode, there’s very little beneath the album’s many clichés to suggest insight, let alone the unfiltered honesty of autobiography,� adding that much of the album “devolves into an abyss of electro-neutral bangers.� And that’s one of the nicer reviews.

In a year when pop divas are truly opening up in their work, it’s a shame that Spears choose to play it so safe. Maybe Vegas is her way of flirting with a challenge.

Will the disappointment of “Britney Jean� stop anyone from buying a ticket to her Vegas show? Absolutely not, and Team Spears can safely bet that bodies will pack whatever venue she plays, just on the strength of her star wattage.

It would have been nice, though, to have an album to blast on that road trip to Vegas. Guess “Blackout� will have to do.