There are several reasons that can cause a poor appetite. You can check and analyze them against these:
1. The cat has hairballs in its stomach but hasn't vomited them up. The main symptom is dry heaving.
2. If your cat has an oral disease, you need to observe it carefully, such as loose teeth, inflamed gums, or ulcers. 
3. Digestive system issues: You need to pay close attention to the composition of your cat's food. Research what they can and cannot eat. Digestive problems are usually caused by food.
4. The food you're feeding your cat doesn't suit its taste; you might consider changing it.
