What does one do when your chicken doesn’t eat?

Of course my chickens eat. They are happy to eat duck food. They’re still laying and they won’t touch oyster shell or any of that fancy stuff but they will eat egg shell. One egg shell lasts 3 days for 3 hens.

I leave chicken feed out they avoid it but the food in their run has been going down slowly . All the research tells me they should eat more than this?

What am I missing? Am I doing something wrong here? They don’t get snacks or treats, and they only get duck food because they are thieving little chucks.
Should I give them extra supplements because of this?

Thanks