Why is my cat eating people food from the counter now?

I have a 5 y. o. female cat. She has always eaten dry cat food (and occasionally wet food, but very rarely). She has recently begun getting on the counter in the kitchen and eating people food. She has done this before in the past, but only if we leave something out, like a tasty meat. Now shes eating anything on the counter, such as last night when we caught her tearing a hole in the bread bag. I know shes eating her dry food because we have to watch her around the other cat and the dog. Weve not changed her food or started giving her less, so Im not sure whats up. We are doing our best to keep our food put up, but the bread incident was a first for us. Any thoughts about why she is doing this?