Try switching to another brand if there continues to be resistance after a month. Last year, I took in an iguana parents I had known for a couple of years. I kept hearing about how picky she was. The other iguanas learned to just not bother moving from their places until Iguanita was done or almost done. Truly Problem Cases There are fewer of these than people think.
Iguanas are masters at energy conservation.
They don't do much moving around anyway during the course of a day - they will just do even less when they are not eating. A true problem iguana is one who was sick to begin with, who may not have been well fleshed to begin with, and who may be undergoing treatment for parasites, dehydration, and or metabolic bone disease. They may have been starved, intentionally or otherwise, by their former owners or the pet store. If you've not taken such an iguana to a reptile vet, do so. Forcing a sick and dehydrated iguana to eat hard to digest food could send it into shock, or worse.