As first reported by Us Weekly in December, the "Hold It Against Me" singer, 31, didn't impress TV execs during her stint on FOX series. "Producers wanted her for the long haul, but it isn't working," a source said.
With Spears being paid a reported $15 million, it was time to cut costs. "They paid all that for her to say 'amazing' and offer half-claps," a second insider said. Fellow judge and X Factor co-creator Simon Cowell, 53, "wanted crazy Britney, but he got boring Britney," another source added.
Spears, who joined the program with new judge Demi Lovato, released an official statement Jan. 11. "I've made the very difficult decision not to return for another season. I had an incredible time doing the show and I love the other judges and I am so proud of my teens, but it's time for me to get back in the studio," the pop star said. "Watching them all do their thing up on that stage every week made me miss performing so much! I can't wait to get back out there and do what I love most."
Spears mentored four teens during The X Factor's live shows, with 13-year-old Carly Rose Sonenclar placing second behind L.A. Reid's Tate Stevens. Like Spears, record executive Reid, 56, will not be returning for a third season.