Population density, primarily. More dense means more close contact, and more contact overall comparing areas with public transit to those without.

Not to mention the human toll of quarantine- I live surrounded by a few hundred acres of forest, my cousin in a studio apartment. My daily life has hardly changed since I also work from home. She lives in or near paris, I think, and couldn't go 10 feet past her apartment door without a permit, and mostly got that only for groceries. Even still, she managed to catch it (or a similar disease, since she was refused testing).

Some people on HN love to hate on rural life, but I honestly wouldn't have it any other way.