The problem is complex, but ranching can't and doesn't prevent subdivisions-if that were true there would not be any sprawl in the West at all. Subdivisions are driven by demand, not the availability of land. There are literally tens of millions of acres of land for sale in North Dakota and none is under threat of subdivision. No one wants to live in North Dakota except the people already there. There is no demand.
Low demand has several affects.
First, it keeps land prices low. Low land price means that another rancher or farmer can afford to purchase the land of his or her neighbor and pay off the mortgage running cows on it. As a consequence only wealthy sport ranchers can afford to purchase a ranch or the land is subdivided into smaller, more affordable parcels. High land prices also affect the ability of ranchers to pass on a ranch to the next generation. For example, an old friend of mine grew up on a ranch.