I guess they have to build some other people up to prevent the entire final 12 being completely obvious from the very first episodes.
However, the more cynical side of me has often thought that they now try to have a "shock elimination" at every stage of the competition before the live shows. It seems to have become an XF staple to put through a surprise finalist at the expense of a more hyped and heavily featured one. It's happened to people like John Wilding (and most famously) Gamu Nhengu in 2010, Jade Richards in 2011, Amy Mottram and Christopher Maloney (briefly) in 2012, Melanie McCabe, Joseph Wheelan and Paul Akister in 2013.. Last year was slightly different because of the wildcards, but it was briefly done to Lola Saunders and kind of Kerianne Covell. Now its happened to Jennifer, and give it 24 hours and we could well be adding people like Monica Michael, Lauren Murray, Simon Lynch...
I know they have to show more than the 12 finalists to make a compelling show, but the way they do it lately just seems to be an attempt to have a bit of controversy heading into the live shows.