If you offer a child a choice for dinner, between say, a chef salad or candy - which will they choose?
To chickens, corn is like candy. They will always choose corn first! But it doesn't have everything they need. If our domestic chickens were able to forage in the forest and fields like their ancestors, they'd find all the bugs, nuts, berries, grubs, greens, seeds, grains, grass, leaves, worms, and whatever that make up a complete diet. Layer pellets don't look like any of those things, and IMHO, I think that's why they don't naturally crave it like they would corn, or mealworms and such.
My chickens prefer crumbles. They'll eat pellets, but they waste more. When I offer both, the feeders with crumbles go empty first. Now, if they could produce feed pellets that LOOK like corn or mealworms, I think our chickens would stuff themselves silly.
Just cut out the corn and other treats for awhile. Give them pellets ONLY. Turn them into mash. Or toss them around like 'treats'. They'll eat. When you do re-introduce treats and corn, do it later in the day - so that they have to get the bulk of their nutrition in the first half of the day.
And remember that their balanced feed should comprise 90% of their diet. Corn, scraps, veggies, and other treats should be no more than 10%. I throw this stuff far and wide in their run, so they'll spend hours scratching for it.