Something is wrong with pet food.

I don't think pets eat anything you put in front of them. I've seen animals reject food and treats plenty of times. They like what they like and just like humans, sometimes what they like isn't necessarily good for them. You have to read the labels on pet food and treats just like with human food. Pets can't tell you if they have indigestion from eating something; if you don't see obvious signs you may not realize there is something wrong.