Rabbits help the world by consuming food that is edible but is not necessarily appealing to humans. For instance I scored A LOT of organic carrot greens at the Farmer's Market. Concerned they would go bad before the rabbits got to finish them, I put them in the dehydrator. Voila` carrot top hay. It is a very popular item on the menu. It all part of the cycle since the litter box contents goes into the garden or is given away to other gardeners.
It may be they like dried carrot tops even better than fresh ones, maybe it's the CRUNCH.