The rate of inflation is based on prices in a number of sectors, not only food, and some where increases have been relatively low.
The simple answer is that the price of anything processed is going to be higher because every part of the process is affected by increased costs of production, especially fuel costs.
Pet food = cost of rearing the animals, cost of getting animals to market, cost of getting them to the slaughterhouse, cost of butchering, cost of factory processing and packaging*, cost of distribution to retail outlets, supermarket running costs.
*The price of steel and aluminium soared in 2020. A pet food tin will will be made from steel. Pouches will be made from a mix of plastic (made from petrol chemicals) and aluminium foil.
The simplest thing would be to buy cheaper cuts of meat and cook them in the cheapest way possible.