When people moved from rural areas to more populated centers for job accessibility, cultural and entertainment purposes, the age old way of feeding a pet table scraps and allowing a free running pet to scrounge for food, changed. The concentration of people meant pets and people existed in a more confined environment. Individuals did less and less growing of their own food and more and more processed foods were purchased.
The resulting change of humans purchasing processed foods created the processed pet food industry to begin flourishing in the 50’s and 60’s. Somewhere I read an estimate that over 90% of all the food pets consumed is preprocessed. This accounts for a large portion of the $40 Billion pet owners spend on these furry friends yearly.