On driving factor is the (over)use of antibiotics in animal agriculture. It's weird the article touches this issue in just one sentence...

"Over 70 percent of antibiotics sold in the United States are given to livestock, including cattle, which translates to significant human health impacts."

"Unlike with human medicine, however, antibiotics are often fed to cattle as a preventative measure, rather than as a treatment."

"Antibiotic resistance in cattle does not only affect the health of the cattle, it impacts people as well because many of the antibiotics given to cattle are also used in human medicine. Eating meat or consuming milk from an animal with antibiotic-resistant bacteria may infect a human with that same resistant bacteria"

Citations: National Geographic