Hi,
I have not a single clue - lots of possible reasons but no clue which of them is the real one.
But, in my case, the snakes had been kept on paper towels since the 24th of September and had not eaten successfully on their own but I changed the substrate to shredded aspen on the 18th of November and all three hatchlings involved ate on the 20th of November and at each offering since.
Whether it is the smell, the simple act of changing the tank, the way it affects heat transfer or some other factor I wish I knew.
Once they seem to be on a good steady eating schedule I might try switching some of them back to see if they still eat.
dr del