Because she's been booked terribly ever since they made her GM. And because it's Wrestlemania season and because she is with Dolph who is also being booked terribly. And a whole host of other reasons that fall under the WWE booking fail umbrella.
It was inevitable that it would happen. Through, overexposure, men stopped viewing her as a sex object, but more of a performer and realised that when that is stripped away, she really doesn't bring anything else to the table - certainly not wrestling ability.
Because she turned heel and theres no other female diva or performer on the face side over enough for her to have a good feud. When she was face, she had Eve and Vickie. They shouldve brought in Trish or Lita to put her over at Mania. Right now she just needs to hope they call up Paige sooner rather than later.
Except that's not true. AJ made many appearances outside the ring, while Eve was with the company, and certainly as GM of Raw and then involved in a story with John Cena of all people, trumped Eve in terms of importance on programming.
OBVIOUSLY it's a continuity of her character. She was with Bryan, left Bryan. With Punk, left Punk. With Cena, left Cena. Hell let's go back to NXT - with Primo, left Primo. Quite simply, it's been extended. She was with the spotlight, and has left the spotlight.