Because the show and its producers are invested in her, as they are with all the former idols. They've put a lot of time and money to create the idea that they're superstars. Now they have to rationalize it, with crap like putting Fantasia on the level of Mariah, Whitney and Celine last night.
Lakisha was STUPID for picking two Idol songs in a row. I'm afraid this week will be her swan song.