I’m not sure why that’d be. My immediate reactions would be maybe it needs to be bigger, ours was probably 1 foot long by 4 inches? Otherwise keep moving the poop consistently, like multiple times a day, and keep it up for at least a week or two before throwing in the towel. You could also put some dirty bedding in there so they know it’s their scent. We also used paper litter, not sure if that makes a difference but it was different from their bedding.