It's more efficient to ship grain than cattle, and most cattle still requires feed to get to market size. The whole mythos behind cattle drives was to get them to a location for slaughter and shipping. The same exact thing you said about cattle is the same as grains, except cows require more water external to the grass.Cows also require maintenance above what crops typically do as well. Ranchers are very good at what they do, however it's still a ton of work. Farming is slowly becoming significantly more automated, which is a good thing as less people are interested in becoming farmers.