Because winning challenges doesn't mean much, Instead of picking one winner of the challenge, choose the top 3 or 4 girls who did the best. That way you could better track who is doing well. Since Naima, the last 3 winners didn't win any challenges, so apparently the challenges are overrated.
Also name a winner of the photoshoot and give her immunity from being eliminated. That way if the judges name a winner of Top Model who didn't win ANY challenges or photoshoots, the competition has nothing to do with actual modeling but personally preferences of the judges.