It's nothing personal, she says - just business.
"Kara and I have known each other for years and we get along great," Abdul tells the March 9 issue of OK! magazine.
"But we tried four judges before and it doesn't work."
Abdul is referring to Angie Martinez, the Hot 97 DJ who joined "Idol" as a judge before the second season but bailed before the season kicked off.
Abdul also says the extra person disrupts the flow of the show.
"It takes up so much time for each of us to give our opinion that it slows down the pace of the show," she says.
As for her future on "Idol," Abdul is a little more cagey.
"It is the last season of my contract, and I have so many other things I want to do," she says.