True, but if they did that, the show would become RuRa-centric.
The makers wanted to avoid that, because, given their stupidity and poor planning and a dead CT, they had already invested enough time and money into getting the Challengers onboard, especially that bhukkad Gupta.
Mastermind bol bol kar usko chanay ke jhaad par chadha diye... In fact, except Arshi and Rakhi, none of the Challengers lived up to their terms of the Contract.
The Challengers, in fact, actually distracted the contestants and took their space and limelight away.