If you start out feeding crickets, rather than CGD, it won't be a problem. In your case the gecko has been given only one option and has been conditioned to it. I don't know when the last time you fed it was, but I would bet that if you let it get hungry and not provide CGD, it would start to go after crickets. It just hasn't needed to use the natural instinct to hunt. Hunger should trigger it. You can dust the cricket with CGD to get a scent association.
Since I don't know how you are keeping the gecko, I will just give a few tips that may help with the process.
Keep the gecko in an enclosure that keeps it in close proximity to the prey items.
Keep the temperature in the mid 70s (f).
If you have other crested geckos of the same size, house them together. It forces them to compete for food and increases their feeding response.
If you are using a well balanced product (CGD) there is no real need to worry. Think of this as a learning experience and offer crickets first and CGD after about a month the next time you hatch or buy a baby crested gecko.
Hope this helps.
Of thousands of cresteds that I have had, only one has ever refused crickets into adulthood.
